Shahid,
You mentioned that you "Generating Assets via Asset Template". And that the issue screen is blank (ie. not showing the assets). To me, it sounds like you did not complete the Goods Receipts. After you perform the Goods Receipts, there's an action called "Receive Rotating Items" on the same receiving screen. That will create the Assets and drop it into the Storeroom indicated by your PO. Then you go to the Asset Template and "Apply to Existing Assets", not Generate Assets, and point to the new Assets you just received into Storeroom Inventory. If you had "Generated Assets" via the Asset Template, then you just made a set of assets with no ties to the PO, and not in Inventory, therefore, cannot be Issued.
To confirm, go back to Receiving screen for that PO. Does it say "ASSET" in the Inspection Status column? If so, that means it's waiting for an Asset number to be assigned. Hit the Receive Rotating Items action to create the Assets.