I’ve seen this a couple of times also, now. I’ve been unable to figure out what’s going wrong with the session handling, but I’m hopeful that an upgrade of OpenACS to 5.2.x will resolve it. That upgrade is coming as soon as a couple of the packages we use have been updated to work on the new OACS version (unfortunately, OACS is in a seeming state of decline, as no one is maintaining the vast majority of packages available for it–which means I’ll probably have to do the work to update those packages to work, which obviously takes a backseat to Virtualmin work).