Error: The sign on Quantity and Net amount have to be the same

Hi,

I have a sales order invoiced which I would like to carry out a full return through sales order return form.

When I select the invoice for return and click OK I get the following Error:the sign on Quantity and Net amount have to be the same

What could possibly be the issue?

Picture of a screenshot here: postimg.org/…/

Are you developer or tester ?
If you are developer sure you can debug and check.

The screen shot is not there.

Anyway are you using a return order or is it a sales order with a negative amount? Basically there is difference between the signs on the net amount and the quantity, there should not be. Correct this and it will work.