Creating business partner gives error: Message no. R1091

Hi Experts,

When I am trying to create new BP it is throwing an error message that

" Grouping ZEM has external number assignment, enter a number "

and when i am trying to see the Error information, it is showing that

Grouping ZEM has external number assignment, enter a number

Message no. R1091

Diagnosis

The business partner needs a key to identify it. This key was not specified.

System Response

The system issues an error message.

Procedure

Enter a key in the dialog. If it is a background process or an XML message process, contact your system administrator.

So can any one Explain it what is this Issue?

Thanks,

Krishna.