diff --git a/Remote/Adb.hs b/Remote/Adb.hs
index 5f057178be..24c9ba1887 100644
--- a/Remote/Adb.hs
+++ b/Remote/Adb.hs
@@ -291,17 +291,19 @@ retrieveExportWithContentIdentifierM serial adir loc cid dest mkkey _p = catchDe
   where
 	src = androidExportLocation adir loc
 
-storeExportWithContentIdentifierM :: AndroidSerial -> AndroidPath -> FilePath -> Key -> ExportLocation -> [ContentIdentifier] -> MeterUpdate -> Annex (Maybe ContentIdentifier)
-storeExportWithContentIdentifierM serial adir src _k loc overwritablecids _p = catchDefaultIO Nothing $
+storeExportWithContentIdentifierM :: AndroidSerial -> AndroidPath -> FilePath -> Key -> ExportLocation -> [ContentIdentifier] -> MeterUpdate -> Annex (Either String ContentIdentifier)
+storeExportWithContentIdentifierM serial adir src _k loc overwritablecids _p =
 	-- Check if overwrite is safe before sending, because sending the
 	-- file is expensive and don't want to do it unncessarily.
 	ifM checkcanoverwrite
 		( ifM (store'' serial dest src checkcanoverwrite)
-			( liftIO $ either (const Nothing) id 
-				<$> getExportContentIdentifier serial adir loc
-			, return Nothing
+			( liftIO $ getExportContentIdentifier serial adir loc >>= return . \case
+				Right (Just cid) -> Right cid
+				Right Nothing -> Left "adb failed to store file"
+				Left _ -> Left "unable to get content identifier for file stored on adtb"
+			, return $ Left "adb failed to store file"
 			)
-		, return Nothing
+		, return $ Left "unsafe to overwrite file"
 		)
   where
 	dest = androidExportLocation adir loc
@@ -377,6 +379,7 @@ mkAdbCommand :: AndroidSerial -> [CommandParam] -> [CommandParam]
 mkAdbCommand serial cmd = [Param "-s", Param (fromAndroidSerial serial)] ++ cmd
 
 -- Gets the current content identifier for a file on the android device.
+-- If the file is not present, returns Right Nothing
 getExportContentIdentifier :: AndroidSerial -> AndroidPath -> ExportLocation -> IO (Either ExitCode (Maybe ContentIdentifier))
 getExportContentIdentifier serial adir loc = liftIO $ do
 	ls <- adbShellRaw serial $ unwords
diff --git a/Remote/Directory.hs b/Remote/Directory.hs
index 5cfb702549..b6ef6be96b 100644
--- a/Remote/Directory.hs
+++ b/Remote/Directory.hs
@@ -395,20 +395,22 @@ retrieveExportWithContentIdentifierM dir loc cid dest mkkey p =
 		| currcid == Just cid = cont
 		| otherwise = return Nothing
 
-storeExportWithContentIdentifierM :: FilePath -> FilePath -> Key -> ExportLocation -> [ContentIdentifier] -> MeterUpdate -> Annex (Maybe ContentIdentifier)
+storeExportWithContentIdentifierM :: FilePath -> FilePath -> Key -> ExportLocation -> [ContentIdentifier] -> MeterUpdate -> Annex (Either String ContentIdentifier)
 storeExportWithContentIdentifierM dir src _k loc overwritablecids p =
-	catchDefaultIO Nothing $ do
+	catchIO go (return . Left . show)
+  where
+	go = do
 		liftIO $ createDirectoryIfMissing True destdir
 		withTmpFileIn destdir template $ \tmpf tmph -> do
 			liftIO $ withMeteredFile src p (L.hPut tmph)
 			liftIO $ hFlush tmph
 			liftIO (getFileStatus tmpf) >>= liftIO . mkContentIdentifier tmpf >>= \case
-				Nothing -> return Nothing
+				Nothing -> 
+					return $ Left "unable to generate content identifier"
 				Just newcid ->
-					checkExportContent dir loc (newcid:overwritablecids) Nothing $ const $ do
+					checkExportContent dir loc (newcid:overwritablecids) (Left "unsafe to overwrite file") $ const $ do
 						liftIO $ rename tmpf dest
-						return (Just newcid)
-  where
+						return (Right newcid)
 	dest = exportPath dir loc
 	(destdir, base) = splitFileName dest
 	template = relatedTemplate (base ++ ".tmp")
diff --git a/Remote/Helper/ExportImport.hs b/Remote/Helper/ExportImport.hs
index 84d3b7c6da..2ae1343752 100644
--- a/Remote/Helper/ExportImport.hs
+++ b/Remote/Helper/ExportImport.hs
@@ -57,7 +57,7 @@ instance HasImportUnsupported (ImportActions Annex) where
 	importUnsupported = ImportActions
 		{ listImportableContents = return Nothing
 		, retrieveExportWithContentIdentifier = \_ _ _ _ _ -> return Nothing
-		, storeExportWithContentIdentifier = \_ _ _ _ _ -> return Nothing
+		, storeExportWithContentIdentifier = \_ _ _ _ _ -> return (Left "import not supported")
 		, removeExportWithContentIdentifier = \_ _ _ -> return False
 		, removeExportDirectoryWhenEmpty = Just $ \_ -> return False
 		, checkPresentExportWithContentIdentifier = \_ _ _ -> return False
@@ -154,8 +154,10 @@ adjustExportImport r = case M.lookup "exporttree" (config r) of
 					oldcids <- liftIO $ concat
 						<$> mapM (ContentIdentifier.getContentIdentifiers db (uuid r')) oldks
 					storeExportWithContentIdentifier (importActions r') f k loc oldcids p >>= \case
-						Nothing -> return False
-						Just newcid -> do
+						Left err -> do
+							warning err
+							return False
+						Right newcid -> do
 							withExclusiveLock gitAnnexContentIdentifierLock $ do
 								liftIO $ ContentIdentifier.recordContentIdentifier db (uuid r') newcid k
 								liftIO $ ContentIdentifier.flushDbQueue db
diff --git a/Remote/Helper/ReadOnly.hs b/Remote/Helper/ReadOnly.hs
index 7cc3f7c14e..aad37b9f61 100644
--- a/Remote/Helper/ReadOnly.hs
+++ b/Remote/Helper/ReadOnly.hs
@@ -65,18 +65,17 @@ readonlyRemoveExportDirectory _ = readonlyFail
 readonlyRenameExport :: Key -> ExportLocation -> ExportLocation -> Annex (Maybe Bool)
 readonlyRenameExport _ _ _ = return Nothing
 
-readonlyStoreExportWithContentIdentifier :: FilePath -> Key -> ExportLocation -> [ContentIdentifier] -> MeterUpdate -> Annex (Maybe ContentIdentifier)
-readonlyStoreExportWithContentIdentifier _ _ _ _ _ = do
-	readonlyWarning
-	return Nothing
+readonlyStoreExportWithContentIdentifier :: FilePath -> Key -> ExportLocation -> [ContentIdentifier] -> MeterUpdate -> Annex (Either String ContentIdentifier)
+readonlyStoreExportWithContentIdentifier _ _ _ _ _ =
+	return $ Left readonlyWarning
 
 readonlyRemoveExportWithContentIdentifier :: Key -> ExportLocation -> [ContentIdentifier] -> Annex Bool
 readonlyRemoveExportWithContentIdentifier _ _ _ = readonlyFail
 
 readonlyFail :: Annex Bool
 readonlyFail = do
-	readonlyWarning
+	warning readonlyWarning
 	return False
 
-readonlyWarning :: Annex ()
-readonlyWarning = warning "this remote is readonly"
+readonlyWarning :: String
+readonlyWarning = "this remote is readonly"
diff --git a/Remote/S3.hs b/Remote/S3.hs
index 3291a7714a..a79712e318 100644
--- a/Remote/S3.hs
+++ b/Remote/S3.hs
@@ -575,7 +575,7 @@ rewritePreconditionException a = catchJust (Url.matchStatusCodeException want) a
 --
 -- When the bucket is not versioned, data loss can result.
 -- This is why that configuration requires --force to enable.
-storeExportWithContentIdentifierS3 :: S3HandleVar -> Remote -> S3Info -> Maybe Magic -> FilePath -> Key -> ExportLocation -> [ContentIdentifier] -> MeterUpdate -> Annex (Maybe ContentIdentifier)
+storeExportWithContentIdentifierS3 :: S3HandleVar -> Remote -> S3Info -> Maybe Magic -> FilePath -> Key -> ExportLocation -> [ContentIdentifier] -> MeterUpdate -> Annex (Either String ContentIdentifier)
 storeExportWithContentIdentifierS3 hv r info magic src k loc _overwritablecids p
 	| versioning info = go
 	-- FIXME Actual aws version that supports getting Etag for a store
@@ -584,20 +584,18 @@ storeExportWithContentIdentifierS3 hv r info magic src k loc _overwritablecids p
 #if MIN_VERSION_aws(0,99,0)
 	| otherwise = go
 #else
-	| otherwise = do
-		warning "git-annex is built with too old a version of the aws library to support this operation"
-		return Nothing
+	| otherwise = return $
+		Left "git-annex is built with too old a version of the aws library to support this operation"
 #endif
   where
 	go = storeExportS3' hv r info magic src k loc p >>= \case
-		(False, _) -> return Nothing
-		(True, (_, Just vid)) -> return $ Just $
+		(False, _) -> return $ Left "failed to store content in S3 bucket"
+		(True, (_, Just vid)) -> return $ Right $
 			mkS3VersionedContentIdentifier vid
-		(True, (Just etag, Nothing)) -> return $ Just $
+		(True, (Just etag, Nothing)) -> return $ Right $
 			mkS3UnversionedContentIdentifier etag
-		(True, (Nothing, Nothing)) -> do
-			warning "did not get ETag for store to S3 bucket"
-			return Nothing
+		(True, (Nothing, Nothing)) -> 
+			return $ Left "did not get ETag for store to S3 bucket"
 
 -- Does not guarantee that the removed object has the content identifier,
 -- but when the bucket is versioned, the removed object content can still
diff --git a/Types/Remote.hs b/Types/Remote.hs
index 282a38c0c9..18ae88a022 100644
--- a/Types/Remote.hs
+++ b/Types/Remote.hs
@@ -292,7 +292,7 @@ data ImportActions a = ImportActions
 		-> [ContentIdentifier]
 		-- ^ old content that it's safe to overwrite
 		-> MeterUpdate
-		-> a (Maybe ContentIdentifier)
+		-> a (Either String ContentIdentifier)
 	-- This is used rather than removeExport when a special remote
 	-- supports imports.
 	--