My understanding of ありませんと is that it is an abbreviated form of ありませんと(だめ/いけない/ならない), but the formal ません throws me off. I was under the impression that the formal part should be always the last one, so it should be ないと(だめです/いけません/なりません). Is it possible that abbreviation moves the formality before と? Are the following interpretations possible?
... must be
... must have something