interface elements generating negative matrix diag ratios

[Breezer]

I recently had a NASTRAN model with CQUAD8 shell elements. The model was perfectly correct, but I still got the FATAL MESSAGE 9050. I then changed the CQUAD8 to CQUAD4 and the model ran through. A possible explanation for this as follows:

... boundary consists of p-element edges along an interface. These interface elements may generate high or negative matrix/factor diagonal ratios. If there are no other modeling errors, these messages may be ignored and PARAM,BAILOUT,-1 may be used to continue the run.

I thought this is just true for GMBNDC, GMBNDS ...

I'd appreciate your input.
Thanks.