INTERNAL PROGRAMMING ERROR # 251

Hello,

I am running a random analysis on a big model and i believe the prepossecing has been done correctly (first  Rnd.An on Optistruct). But apperently it hasn't and i am unable to understand the following error message:

*** INTERNAL PROGRAMMING ERROR # 251 ***
  Specified vectors (717 - 717) out of range (1-716).
 

What is it talking about exactly so i could go and check it?

Thanks

PS: share fem file. output if needed