The selected location is not assigned to the project that is specified in the purchase order.

Here’s a couple things to check:

• Is the item still in inventory or has it been issued to the project?  If it’s been issued to the project, you’ll need to do an inventory receipt to receive it back into stock before returning.
• Do you have the correct cost layer type selected (Normal/Free Stock vs. Project) if you are using project specific inventory? 
• Do you have the correct warehouse and warehouse location for this serial number?

​@trungrigshop This article Might be helpful for you!

2. Hi Megan,
   
   1.  The item is already issue to the project and I did Physical Inventory Count to bring it back with the exact cost and Lot/Serial Number.
   2. I would assume you are talking about PO type which is “Normal” or Inventory Source in Issue is “ Free Stock”
   3. The warehouse and location should be correct cause I only use one warehouse and location for the whole system.
    

Thanks for recommendation, but I saw on mine the warehouse and warehouse location is the default one which we always use and it has just has problem since yesterday.
Is there anyway that I can check warehouse and warehouse location in Project and Task

Maybe you can check if the Location you try to return was link to Project or Not. Even it liked or didnt, make sure the Receipt and Return was the same. Example: on Receipt, Location was link to Project, as the time do Return, Location should link to Project too