Geoff, that didn't work. I keep going around in circles - log out, reset cookie- didn't reset -try logging out......
I assume that, because the cookie is there, it won't reset, but somehow Mudcat doesn't recognise it.

Are cookies on the computer, or are they in the browser? I'm reluctant to remove them manually, in case I can't get on at all.

I did a full virus scan yesterday.
I'm assuming that Max is altering Mudcat so that guests can't post, because (on Opera) I have no submit button and no search box.