Error message hard to understand when sync client is blocked

[schiessle]

As long as the user didn't accepted the ToS, access to the files is blocked by the sync client.

The user gets a sabredav error from the desktop client, something like "file not available". A normal user will never figure out what's the problem and how to solve it. It would be great if we could show a error which tells the user that they have to go to the web interface and accept the ToS to sync their files again.

Maybe the ToS app could through a exception with this error message which than gets forwarded to the clients?