I still have the exact same problem.
A pre-existing library (encrypted or not, created with a 2.x server).
When i try to upload new files, i get this "error occured in upload" message, with
- windows client 3.0.2
- linux terminal client 3.0.1
- linux terminal client 3.0.2
and server side with : 3.0.1 and 3.0.2 (i upgraded everything to see if the latest versions resolves the problem, seems it's not fully corrected yet).