大神们帮忙看看用optistruct后处理时提示这个错误

meliuyang1018

用3D—connector—spot定义的接触，这两个零件之间是焊接的，简单约束施加载荷后用optistruct分析后，提示如下错误

为什么？

*** ERROR #  724 ***
  An invalid rigid element.
  This RBAR has rotational rigid body modes in all three directions.
      RBAR element id =     211255
  independent grid id =      16574
    dependent grid id =      32478
  Note: If this rigid element is also connected with other rigid elements,
  then this error means that there is rigid body mode or mechanism remained
  in this rigid element chain due to lack of connected structural elements.