Original Slide Remote Problem

I'm having an odd problem with my original TiVo slide remote, which I use with my Series 3. For no good reason (not dropped, not otherwise damaged, batteries are fine), a couple of days ago, it simply stopped controlling the TiVo. Since I don't have the dongle anymore, I was only using it over IR... but it still controls both my TV and my receiver over IR, even from clear across the room, so I know its IR emitter is working fine. I also know the TiVo is responding properly to IR, as I have a battered old remote (the one it originally came with in 2007) that, despite missing some of its plastic, can still control it.

I tried resetting the slide remote, on the chance that perhaps it had somehow been locked to a different DVR "channel" than the one I'd been using, but that didn't help.

Anybody have any suggestions as to what might cause this, and whether there's anything I can do about it?

Thanks!