I've been searching all over for suggestions about a problem. I recently purchased a GOG download of RollerCoaster Tycoon 3 and while it has downloaded successfully and I've played it for a day without a single problem, the game does not load saved games and an error message pops up stating that the game has failed to load. I have tried running it on Compatibility XP Service Packs 2 and 3 and also run it as an administrator, like suggested in many forums. However it still crashes upon loading a saved game. Anyone have any suggestions?

RCT3 sometimes has problems loading big parks or parks that had custom flatride added and removed. There's a community tool called Park CleanUp that can help solving these issues. Here's a thread in a RCT community about it.

There might also be a backup of your park. Usually you'll find the saved park under My Documents in a subfolder of \RCT3. The backup of your park has the same name but the extension .bak (e.g "My Park.dat" and the backup file "My Park.bak"). If you don't see the file extensions, then they're hidden (see here for instructions how to show them). Rename the .bak-file to ".dat" and try to load this one instead (maybe the newest save is corrupted).