Invoicing against a release

using ver 6

we have the following issue and need to know if we are missing something or ?
We are invoicing an item with multiple line releases, I am now up to invoicing the third line release; but it is not an availbe option in my invocie enrty screen, this line was not previously invoiced against and is shown on received not yet invoiced report.

the line release is visable and it does show the correct packing slip number and line release number.