Capital Projects - Split asset lines with invoice and credit note

Hi,

System: Oracle R12 - PA Capital Projects

When trying to split asset lines through Capital Projects I need to split into one invoice and one credit note and when I enter either of them, the invoice takes it over the unassigned amount and the credit note takes it below 0. When trying to enter either of them, it returns an error message stating "you have entered an invalid split amount" as per below screen shot.

The credit note relates to an existing asset that has been previously capitalised.

The invoice is a separate asset to be capitalized

How can I split these values and capitalize the credit note separately?