No restrictions, however you will be best served by providing an expanded SASLOG pasted in a forum post reply, so others can help guide you with the specific error condition and message text. Be sure to add:
OPTIONS SOURCE SOURCE2 MACROGEN SYMBOLGEN;
Also, the above diagnostic command added to your SAS program may help with self-debugging.
One hint is that SAS data variables must start with an alpha character, so until we can see what macro invocation parameters you are supplying when invoking %gen, it's difficult to identify the problem cause. Suggest you first add the OPTIONS statement, rerun your SAS problem and review the SASLOG - then reply with more information if unable to determine the cause.
Scott Barry
SBBWorks, Inc.