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I'm sorry to hear about your problem with the "no valid security token errors." I can empathize with you because though my problem with this is not nearly as bad, it certainly could be a site killer and sounds like it in your case.
I've been dealing with this for a long time and have reported it as an official bug but it has not been "assigned" to anyone and I have not heard any responses as to how to fix it or even start to track down the problem. It seems to be a problem that is isolated to specific, limited sites (perhaps server configurations) and impacts site functions differently in each case, like comments, notifications, log-in, registration, browser types, etc., depending on who knows what.
I upgraded to 2.3 and don't know if I still have the problem or not. My users don't bother telling me about it anymore as it only relates to comments on Firefox. Go figure.
My sense is that the problem, though highly significant for those that it impacts, is very limited in the number of xoopsers affected and therefore is not really getting attention. Also, my guess is that the security token function may be something that only a few XOOPS devs really have experience with. Not sure where you should go for help, but let us know if you find it or can raise this issue up higher on the priority list.