You could do 'symdg exportall -f ' to export the group information to a file.  Then check the devices by doing a symdev show of each.  Chances are some are RDF (R1 or R2) and some are not.  If the group is a type 'RDF1' for example, all source devices in the group need to be R1's.  If any are not, you'll get an invalid group.
I'm searching for a SYMCLI command for info about an invalid SRDF-group. With symdg show DgName and symrdf –g DgName que, I get no result.05/31/2013  14:29:02.254   7304   7384 EMC:SYMRDF  emcSymValidateGroup Group: (GroupName) is invalid because there are mixed type std devices; 
SYMCLI command SRDF - info