RTV with Shipping function

Hello All:

We would like to use Return To Vendor (RTV) with shipping function but finding the process is working for some items, and not others.

II thought it may  have to do with Inspection Required, but it works for some but not others,

Then I thought may be serial controlled is the issue, but same result

Then may be because we didn't return from the same subinventory that we received, but same result.

Any ones know of any restrictions that you can share with  me?

Thanks,

Sanday