Error:
"Invalid group condition."
or
"This group section cannot be printed because its condition field is nonexistent or invalid.  Format the section to choose another condition field."


This Bug arise only if you have bad group sectors like
i) Please do Database-> Verify Database
ii) Please check your Dataset provided to the Report for the actual field exists or not.
iii) Remove unused Group from your report

it will gone permanently...;)

Happy Coding...