Sounds like a Windows protected folder issue.
If you use folders that Windows had set up like Programs (x86) or desktop, user, etc. Windows will prevent unknown programs (TSRE) from writing to those folders.
Best to use folders like C:\Trains or E:\MSTS that you create outside of any system folders. You have control of those, not Windows.
Randy
Wanted to add. MSTS content, Openrails and TSRE need their own folders. They do not comingle well at all.
Such as. C:\MSTS, C:\TSRE, C:\OR. You use what works for you but keep them separate.