Update: Reinstalling both the installer and the current version of the viewer fixed the issue. Huzzah! I couldn't figure out why a new dance gesture wouldn't loop on the review server, no matter what I changed in the settings. It would play once, just fine. Then the animation stopped but the "Stop Looping" button was still present. Then I tried an existing (working) animation.That one wouldn't even play. I logged onto the Live server, and a similar issue happened. An existing gesture/animation played once but failed to loop. After waiting quite a while I tried another gesture. The avatar bopped into the ground and back up but never began to play the gesture animation. I tried a third animation on Live. The avatar moved it's feet briefly but never started the animation. I cleared the viewer cache and tested on both the review server and the Live server again. This time the Le Custard animation played once then the avatar stood and the looping stopped. I clicked the Stop Looping button. The animate camera box stayed on the UI screen for some time. After that no other animations would play longer than a blip in the avatar, as if it was trying to move but couldn't start the animation. I'm going to assume for now that my new gesture is OK, since existing gestures are also affected.