Can't convert Received Item to Bill

Hi,

I am having Issues when I try to convert a received purchase order to a bill. It comes up with the bellow error

1st Error Message that comes up

Then if I try to retry the below error comes up.

2nd Error

I have tried re-entering as a new bill all the items and still get the same errors.

I have sold some of the items that have been received so urgently need help to fix please :)