My business mgmt app suddenly can’t write to its own Temp Fule Foldet

My business mgmt and accounting all has been flawless since 2009 from vista to 10, since Jan 2018
It’s a dual app: a separate server and a Netwirk app in the same pc. You open the network app to add/ retrieve / edit data, that’s stored in the server app.
2 weeks ago I started getting Random Errirs: “can’t access or write to the temp Folder ( that’s part of the business app). At present , screens don’t accept dara, it I can’t chsnge to the next screen, it it just quits
The software co remotes in, reinstalled everything, STILL SAME ISSUES!
They think the 3 antivirus sois that came with the Dell PC, are the cause, & suddested I like n’installez them 1 at a time to see if this is the fix?
How do o do this?
Where do I copy them to fit a later reinstall?
Art Suggs as to the actual problem causing thus? Thanks

A lot of anti virus will stop writes to temp as a lot of virus write there. You shouldn't have three av as they just block each other try removing them