Using owncloud 8.2, when adding a new user it can error saying that the user already exists, regardless what username you put in.
This turned out to be a problem with an App called “User backend using remote HTTP servers”, disabling this resolved this error for me.
If you are using the standard ownCloud authentication method then this App should not need to be enabled.
I use the Owncloud client to synchronise important files between my laptop and desktop computers. Recently the client failed immediately on start-up with the error “csync failed to create a lock file”. To resolve this issue, locate and remove the lock file.
On version 1.2.x the lock file can be found in the following locations, depending on which OS you are using.
Take heed: Left-over “stale” lock files are usually safe to remove, however if multiple instances of the same program are running, such as in a separate user session, removing the lock file can cause write-conflicts and corrupt your data, so be warned! Only remove the file if you’re sure it’s not being used by another running instance of the Owncloud app.
Thanks to Markus for providing the Mac OSX location