Has anyone else had this problem? Any solutions?
GOG is aware of certain games having issues, they've fixed some and removed the updates for others. SimCity 2000 is not currently on either list though as far as I know.
One user reported using "Verify/Repair" function worked (which I assume must be a Galaxy feature, if you're using Galaxy).
Otherwise, I'd suggest posting in that thread to let GOG know it's not working.
It wasn't working for me either but a Verify/Repair function worked.