@SILROZ3516 It seems like you have already cancelled the connected PO as the Requisition line status is Released. To Cancel the PO, Receipt should have been cancelled. Meaning that you must have unissued the issued materials from WO as well.

In such scenario, generally the application should allow you to delete the requisition line disregarding the Cost lines.

The shown error message appears as a result of the checks for cascade deletion (when you try to delete the line in the Materials tab as these are directly connected to Work Task Cost records which cannot be removed/ restricted.)

But here it seems like you had some additional steps, can you please provide more info including the UPD version as well?