I removed material from a BOM but still unable to change UM.

I created 2 new materials, and used one on the BOM of the other material. I have not made these active yet in SAP, they are still in engineering mode. Now I need to change the base UM for one of them, but get error message that it cannot be changed due to being used on a BOM. I removed that material from the BOM, but I still get the error message. How do I change this UM?

Thanks!