Trying to save - "Access denied"

I'm training a coworker in editing some html files, but the files won't save. The files are on a shared server in the office. I created the files with DW CC 18. My coworker is using DW CS 5.5. I tried this on a different computer with DW CS 5.5 and it works fine.

Me: Windows 10, DW CC 2019 - everything's fine

Coworker 1: Windows 7, DW CS 5.5 - "access denied"

Coworker 2: Windows 7, DW CS 5.5 - everything's fine