EDIT:  Oops, I missed that you said SEP, I read it too quickly.  Offhand, I don't remember how a SEP for a Partnership works.  Sorry.

Original comment:

Double check that you entered Box 14 of the K-1.

If Box 14 of the K-1 is blank, WHY is it blank?  If they were working for the Partnership, there should be a number in Box 14.