Files opening read only and cannot drag and drop materials

Hi, 

How do you stop a file becoming read only? I don't know why but when I import FBX files substance painter suddenly is changing to read only files, and I cannot drag and drop any materials onto the meshes. 

I literally can't do anything now in the program. I've tried running as administrator, tried going back to the previous version (which worked without issue), tried opening different FBX files - nothing changes.