Does this implementation include Project Budgetary Control? Have you enabled Encumbrance Accounting?
In case you do need that functionality, go on and complete the implementation steps.
Assuming you don't need that functionality do not tick in the checkbox for reserve on the requisition line.
Please check the Budgetary Controls in PA and Encumbrance setups on Account Setup Manager > Advance Options : "Enable Budgetary Control" + "Reserve for Encumbrance Account". You also need to set WF for Budget Accounting.