If you have Unavailable Stock showing against a code, it means that there is stock being used by another area of the system.
Unavailable Stock will remain in this status until associated reports have been Completed.
Check that you have no Outstanding Customer or Supplier Returns for the code.
If you wish to make the stock available by removing the allocation to the return, you will need to go to the stock code- Balances>Batch Records. In the batch record you will need to change the Warehouse of the Unavailable Stock to Goods Inwards