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ERROR # 772

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Hi All,


I am trying to run an analysis on a pipe section subjected to torsion.

When I run the analysis I get the below message


***There were 4 error messages during input processing***

  The first message is repeated below:


  *** ERROR # 772 ***

  It is invalid to use a free grid as an independent grid in RBE3 data.

  Free spiders are not allowed to be independent grids in RBE3 data.

                 RBE3 id =     4903

            free grid id =     9634

     weighted components =      123

  You should remove this grid from the RBE3 data.


 *** Run terminated because of error(s) in the input data.


Does anyone have any advice to resolve this error?


Thanks in advance,



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Hi Luke,


The error would generally be because of RBE3 nodes that are not connected to any part of the structure, this would create singularity in the model and hence OptiStruct throws the error message. you can repair this manually or


We have an automatic way to fix this starting from 13.0 using a Param card, PARAM,RBE3FREE,YES.


12.0 - you can add the below debug card to overcome this issue ( Analysis > Control Card > DEBUG) with version 12.0 or before


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Independent node on RBE3 should not be free. It should be connected to another element. 


Try to figure out this or you can use RBE2 instead. 


In version 14, go to Control cards>> PARAM>>RBE3FREE>> YES

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