Two attributes refer to same IBA definition

Hi.

I have a situation with two attributes referred to same IBA. To delete one of them it should be removed from layouts. But i have next error when i try to delete one of them from layout:

"Attributes *** and *** on ru.sniihim.DefaultEPMDocument refer to the same iba definition"

How can i solve this problem? Windchill verison 10.1

Thanks.