When you uninstall the game, check if it has erased whole Space Empires IV directory. If it didn't do it manually. You may have corrupted file there.
Also check for viruses and do a scandisk.
I have had the same problem where I could not re-load a saved map. As it turns out I had to create a new map first, this then allowed me to load a saved map. Try that and see if it helps.