Hi Rajesh,
I am assuming that you have already linked the PM order to WBS element.
Check the budget profile / tolerence limits assigned to WBS element. Is it in error mode for all transaction types? as listed below..
++ All activity groups
00 Purchase requisition
01 Purchase order
02 Orders for project
03 Goods issue
04 Financial accounting document
05 CO document
06 Budgeting
07 Funds reservation
08 Fixed prices in project
09 Payroll
2. Are you just creating reservations on PM order? As accounting documents are posted only when Reservations are issued (actual cost gets posted) you will get error at that point.