Encoding fails always after one file

I'm using Adobe Premiere Pro 2020 to postprocess a lot of clips. The rendering is done within AME 2020. It is a very long list of jobs to do. When I start rendering, AME renders the file on top oft the list but the fails for all the other ones. The error is "Reading from source not possible" (In german: Lesen von der Quelle nicht möglich. Prüfen Sie, ob diese verschoben oder gelöscht wurde.)
When I close and reopen AME and reset the failed files, it will again render the top file (without any change in the settings). The next ones fail.

I've already tried to log off the cloud and log in again, but this didn't help. Same when started AME as administrator.

Any ideas?