Change of UOM in material master?

Dear SAPIENTS,

I created a material with UOM (M)just now and than assigned to inspection plan. Now I am changing the UOM of material to Nos.. I was getting following

Error: The base unit of measure cannot be changed

The reasons for this are

Routings already exist that are assigned to the material.

RType RtgGrp GpC Plant

Q QRW6MTQT 1 1100

SO I removed the material from inspection plan. But still I am getting the same error. Can anybody tell me the reason behind it?

Regards,

Kaushal Rai