SRM PO: Account assignment category cannot be changed for limit items

Hi All,

I have having issue with PO. We are using SRM7.01 ext.classic.

While changing the Purchase Order i got the following error message in RZ20

"Account assignment category cannot be changed for limit items"

Purchase order is not having the follow-on document.

Purchase order is not a limit item

Not changing any account assignment.

Kindly let me know the solution.

Thanks,

Raju