Copying 261 Movement type

We have created a new movement type Z61 by just copying from 261, but while using the new movement type Z61 in MB1A, it is giving dump error as follows

"The system is trying to interpret Z61 as an integer … the first line of the dump

“Unable to interpret "Z61" as a number.”

Could you pls. help me out , what exactly gone wring

Kind regards - P.L.Dey