I have no idea what is your specific problem. And if I see such problems on our design, the procedure is always the same:
1) close all Mentor tool and reopen only DxD. Do a diagnostic Tools-->DxD diagnostic. If there are errors click and let them correct. Close the design and reopen and repeat until all error are eliminated through diagnosti.
2) Repeat the same procedure with CES. Open CES and do a tools-->CES diagnostic. If inconsistencies are revealed let the tool fix them. (click to fix)
3) the last thing I do is use Start->all programs--> Xpedition Enterprise-->System Tools-->iCDB Project backup. Then if possible try Project -->Repair.
This solves most of the time most of the errors.
If not, call support.
Hope this helps