I have had that happen a lot. I bet some files were probably corrupted at some point before, during, or after the download process. This is one reason why you should save some back up copies of the scenario as well.
When I use to play RCT2, this occured sometimes when I put a specific rollercoaster in my parks. Each time the coaster came into view, the computer would crash and give me the error message. Some how that file had become corrupted.