GRN reversal

Dear Sir

Inspetion is active for material type ROH.UD is made for inspection lot and stock is transferred to UR.After that due to some problem , we want to camcell the GRN.So again stock is taken back to QI by activating inspection type 08.Then also we are not able to cancell the GRN?Also why at the time of cancelling the GRN, "STOCK TYPE' field is disablled? How to make it unable ? Also during cancellation of GRN it is giving the error "You cannot cancel GR, since inspection lot is already partly posted".How to cancell the GRN ?

Thanks,

Sachin