Field change Activity Unit is not possible (transaction data already exists)

Hi ,

I changed unit of measure in activity type (KL02) system is given error message

"Field change Activity Unit is not possible (transaction data already exists"

In OBA5 , I switch off error message , so that system accept to change fields in dev, but it is not working in quality server.

So what is missing on my configuration. Kindly guide me.

Regards

Dharmendar