Every AddOn tells me "500 Internal Server Error"?!?!

Hi. I wanted to use the SMB-Backup-Tool and have seen “500 Internal Server Error” in the logs from the Add-On. I checked other Add-Ons - the same.
Also after uninstalling the SMB-Backup-Add-On still “500 Internal Server Error”.
Can someone tell me, how to fix this?
Thanks