Hello Christian,
If your PC is still Windows 7? I have seen this error message many times, one of the reasons is that the user has WIN 7 Pro, in fact, it is not fully tested/supported by FEFLOW 7.4.
Please refer to the release note: https://manuals.mikepoweredbydhi.help/2021/Release_Notes/FEFLOW%20Release%20Notes.pdf
Best,
Jintao