Hi @SimplyCrazyDev ,
What's your application pool identity? Consider that differences between IIS and IIS express, I think the issue may be caused by permission. IIS express has high privileges to run programs, just like an administrator. But the default identity in IIS is application pool identity. This is a virtual identity created after application deployment, with very low permissions.
So I think you can try to change identity of app pool to local system or administrator, check if it still reports error.