Program fails to start on one profile but works fine on another.

This is for a work PC. We run Stamps.com as an app and it has been working fine for several weeks since this new PC was installed. Suddenly, the Stamps.com app fails to start on the primary profile on that workstation and gives two error reports which I will attach here.
I have uninstalled, reinstalled, repaired and reloaded the Stamps.com app and get the same result each time. However, when I log in with a different profile with the exact same permissions, it works fine. Ok, so it's a problem with that domain account. Well nothing has changed with the account, so I log into a different workstation with the profile that did not work on the first PC, and Stamps.com works fine. I am totally stumped.
Looking at the error reports, it looks like a mscorlib.dll problem or a .NET problem. I replaced mslibcor.dll from another machine that worked, I updated and rolled back the .NET framework.

For clarity:
PC1 > Login1 = does not work
PC1 > Login2 = Works
PC2 > Login1 = Works
Error messages mentions mscorlib.dll, replaced file from PC2, no change.
Error messages mention .NET Framework, upgraded and downgraded .NET framework, no change.

I am pulling my hair out over this. I have found several other posts in various places regarding this problem, but they never actually mention a solution.

I feel a little insulted that you assumed I don't know basic troubleshooting. The page you linked along with all the other Stamps.com tech support pages I have looked at do not apply to my problem. Since my first post, I have even contacted Stamps.com tech support by phone and they were unable to assist me as well. This is not a simple issue or a common problem. I can tell that I am not the first person to have this issue as I have been able to find some other posts, here and in other forums, about this problem but they all lack a solution.

If you can suggest a specific route that I can explore or point me towards documentation that is relevant to my problem, I would be very grateful.

I appreciate that James, and I also might have reacted a little more rashly out of frustration than you deserved.
Hope you have a great day :)

NTN said:

Are there also other apps or programs on this PC1 that have problems or is it just Stamps?
Could be useful knowledge to try to identify the problem.
The way I read it, it's probably only Stamp, so the problem could probably be in this app instead of Windows, .Net Framework, Runtime etc...

No answer....ThankYou.

Yes, it is only Stamps that is having this issue, however that is basically all that PC is used for.

Talking to some other sources, they think the problem might lie within Windows Update making some tiny changes on the more modern machine that the older machines can't support that is making it blow up. I am going to explore this and I will get back with an answer.