Help request: can't share to Exchange

I built a great little house - 'little' being the operative word; it's for antisocial Sims living off-the-grid. I really want to share it (or at least back it up!) but I can't upload anything to the Exchange.

It doesn't even launch the Uploads option; as soon as I click 'share' it sits and thinks about things for a while and then tells me that it failed to upload to the Exchange.

Anyone know how I can force it to generate a simspack for me? I'd hate to lose this hard work if anything goes BOOM in the future.