Getting orders from Pending to Complete

[FrazerPart]

Can somebody tell me what I am missing!
I have an order that states it's pending. It isn't anymore because I have received and processed a payment (Payment Sent Seperately) and I have shipped the items.
I have told Actininc that payment has been received in full - i.e. there is no outstanding balance and I've set the single line item to show it's 100% shipped.

What am I missing?

If I highlight the order in the pending screen and mark it as complete, I get a warning about extra payments/refunds....regardless of clicking yes or no, the order will still not switch to complete.

Come on guys, where am I going wrong?!

[TraceyHand]

has an invoice been printed?
I believe an order won't move from pending to completed without printing and invoice (even if only to .pdf, if you don't require a paper copy)

[guccij]

It doesn't physically have to be printed - you can tick "mark packing list/invoice printed" in the order processing options.

[TraceyHand]

It doesn't physically have to be printed - you can tick "mark packing list/invoice printed" in the order processing options.

if you use the 'one click order completion' option. Yes.
(Settings > Business Settings > Order Processing )

[FrazerPart]

Thanks everyone - it was the invoice printing issue that was causing the problems