This error can sometimes happen when upgrading resources when upgrading between different editions (Enthusiast -> Professional, Professional -> Workshop, etc).

What you can do is clear your local cache and force a re-fetch from the server, the steps are as follows:

1. Close PCMTec Editor.
2. Win + R.
3. Type %appdata%.
4. Locate the PCMTec folder and rename it to PCMTec.old.
5. Restart PCMTec Editor.

 
Enter your credentials and it should query and download the assets for your upgraded Editon.