Did you open Crystal Reports from the START _ PROGRAMS ? OR from within Simply? apparently, opening Crystal independant of Simply has been known to fix a similar problem. It makes some kind of setting adjustment.
Also, reviewing my cheat sheets, I've seen a reference to "verify the database" from within Crystal before attempting to test things in Simply.
The last thing I can suggest, is to copy the report from the version 7.0 forms folder into the 8.0 forms folder. ( Rename the original 8.0 report first). I've come across one incidence where this fixed the problem.
Best of luck!