Your question is too vague.
Could attach your file so that you can see or the problem lies.
I received this error last month. This may be due to I have given constraints on points and I forgot to attach points to geometry with beam element.
But anyway please send some snapshot to have a look in to that.
Did you try the suggestion Mechanica / Simulate gave you when you got this error? If you run a model analysis it will show you which degree of freedom you are missing.
have you been able to solve your issue with one or more of the answers from the thread (or otherwise).
Please let us know and if a particular answer gave you the right clue, consider marking it as correct.