After installing the new CT versions as mentioned in the above forum, the validation for define.xml no longer works in P21 community 2.2.0 for these CT versions.
The validation of SDTM datasets and SDTM datasets/define together work OK, and discrepancies fire correctly. However, when we try to validate just the define.xml alone without the datasets - we are getting the following error “Uh oh, a serious error has occurred…”