Error when creating PO for a project

Experts,

While creating a PO(Purcahse Order), in general fast tab in reference section i select a project which has a budget of 200,000. when i try to submit the PO. it throws the below error but the PO is submitted. Now when PO is approved and when i try to confirm it. It does not confirm the PO and the below error pops up again.

Error:

The entry for category 'ProjItems' on project 'Test-FP-New-GRP1' cannot be posted/approved because it would cause the cost budget to be exceeded by 100.00

Thanks!