You have not replied so im assuming you found the answer. It'll be nice to share since there are other people who come looking for an answer for the same problem. So im just gonna answer anyways though this thread seems inactive. I'm new to Femap as well and I do encounter this issue from time to time. In my experience this error usually occurs when the model is not constraint properly. Check all the constraints again. If the model is huge, then just add the following parameters to the nastran code (bulk data file) and run it again:
PARAM, BAILOUT, -1
This will force the analysis to continue despite the above mentioned error. Once the result is out you can check the deformation and you should be able to identify where the model was not constraint properly as the deformation would be abnormal. This is a very crude method but has worked well for me and hopefully it will for you also.
