In crystal 8.5 some information stored in the report is inacessable or read only via the RDC.
Specifically:
I was not able to add a group using a formula. Thread ID: 643583 "Crystal 8.5 RDC problem adding a group using a Formula "
Another is determining the exact information about type of database connection. In addition most of the formulas stored in the report are not updateable using the RDC.