Hi Bika:

Are you seeing the same error on both servers? Does the error happen in any container with any file type?
Have you checked your site file root (or project/folder file root if set) to ensure it points to a writable location on the underlying file system? Documentation: File Root Options

The best next step is to check the labkey.log for additional details about what is wrong. Repro the error again and then check the most recent logs. Documentation: How to find the logs.

If you aren't sure how to interpret the log errors you see, please attach the relevant portion and I can take a look.

--Molly