It seems prudent to me to look at antivirus protection or others.
It is sufficient that only certain types of files are allowed to be read for the others to be declared in error.
The problem is that everyone goes for their protective layer and it ends up stepping on the toes, W7 + browser + this + that.
Look at the files that are allowed to be read and/or opened.
For GT22 Edrawing works great on a machine that doesn't have SW for example a regular tablet.
Last but not least, in the STEP files, there are several formats and you should try them all to see if there is not this problem. One of my suppliers noticed this because he receives files for his 3D printers from everywhere and from all software (some software does not seem to respect the whole file structure, especially when there are cascade conversions.)