Network budget exceeded error while creating Goods receipt/Invoice

Hi,

I created project , wbs element, and network and released the project...i created a Po using this network...after that i went to CJ30 and allocated budget for WBS element..I activated availablity control check and define the tolerance limits for all transaction groups (++) with usage as 3(Error message) but i am not getting any error message while creating GRN/Invoice...what setting i have to made to check the budget availablity at the time of goods receipt creation and invoice creation....

Thanks

regards

Dinesh.a