Error while solving.

Hi all,

I pre-processed a grillage structure in Hypermesh and when I solve in nastran, it tells the following error:

^^^ USER FATAL MESSAGE 9050 (SEKRRS)

^^^ RUN TERMINATED DUE TO EXCESSIVE PIVOT RATIOS IN MATRIX KLL.

^^^ USER ACTION: CONSTRAIN MECHANISMS WITH SPCI OR SUPORTI ENTRIES OR SPECIFY PARAM,BAILOUT,-1 TO CONTINUE THE RUN WITH MECHANISMS.

I understand that it says since it is not properly constrained, it forms a kind of mechanism so the run terminates. While i tried all I could both in Hypermesh and Patran/Nastran, I don't know why I am getting the same error again and again..

I have constrained the degrees of freedom of the structure in the independant node of a RBE2 element. Load application is also through an independant node of RBE2 element.

I solved with even single node constraint and all failed due to the above error. Can anyone help me to solve this error..?