Hi ehk, I guess your product is managed with negative stock and the delivery, that you try to return, creates pending movements. So try to adjust the pending movement using Stock >  Periodic processing >  Adjustment of stock shortages  

You can use the stock inquiry Suspended transactions to see all movements requiring an adjustment.

Hi Julien, appreciate for your response. Yes I am able to see several suspended transactions and adjust them and successfully return one delivery. But am not able to return the next as I have couple of them. There are no further suspended products to adjust either and I have tried to run stock resynchronization and control and quantity resynchronization as well as account balance to post journal for the successful one yet I am unable to post the next.

Hi @ehk, then I don't know what's wrong you may need to contact your Sage support team.