Error 23

Hello:

I'm very new in Optistruct. I have just done a couple of tutorials about topography design and now I'm trying with some real parts.

In one of them I'm trying to maximize the first natural frequency but the following error occurs:

ERROR # 23 FROM SUBROUTINE renum2

SID 2 is referenced by METHOD,

but is not referenced by any bulk data.

***** FATAL INPUT DATA ERROR *****

How can I handle this?

Thanks in advance for your help.