There have been a few issues with Crystal Reports and .Net. I've learned much from their site:
support.crystaldecisions.com
One such issue had something to do with the fact that if you created a report and initially had the "save data with report" option checked, and unchecked it later, then it wouldn't care. It recommended to resave the report under a new filename.
There are also many patches available for Crystal Reports which fix several issues. Give the website a try, and look at the patches, see if they can fix what you need. Beware though, some of the patches say something to the effect don't install until you read what they will do. I have never had a problem, however.