NX Nastran is using the PCGLSS iterative solver just like NENastran does. The only difference is that NX just added it so my guess is this is a bug in their implementation. PCGLSS is very fast with 10 node tets (typically) so I would imagine their program is trying to use it. Look for a .PCE file somewhere or see if NX lets you specify a different solver. The presence of a .PCE means there was a PCGLSS error and that file should list what the error was but it will not help you as this is for debuging mainly.
