It may possible the SSO or any other service to break after the time out reached in the upload.
After the the break, application pools take time to recover or dead in the state, causing un expected error. Sharepoint log (12 hive\logs) shows the "Error code is: -2147418113' code.
Work Around: Go to the Application pool in the IIS, right click and recycle the pool.
Still not solved, IISRESET. Further error, edit the SSO to be manual.