Hi- if Hrishikesh's suggestion doesn't help- can you look for more information with the FATAL error... see if there is a line with "PROGRAMMER INFORMATION" and send that information to us.
If you are running SOL400 and you want to make totally sure you aren't getting the 'enhanced formulation', you might need to add the following bulk data command (Nastran has some triggers that automatically convert the elements to the 'enhanced formulation'):
NLMOPTS,SPROPMAP,-1
You also might want to try changing from BAR elements to BEAM elements.
