Message bbp_pd 047 Item 001 WBS element budget exceeded is shown during SC creation but not during PO change

Hello experts,

Message bbp_pd 047 Item 001 WBS element budget exceeded is shown during SC creation, but during PO change in SRM portal this error is not shown. As a result the PO is saved in SRM but cannot be transferred to ECC because of the budget exceeded error. Why could this be happening?

Thanks in advanced,

Jack