Tried a few more things, like going back to an old backup. Using a friends settings (Which work fine on his computer!), compacting databases etc. No joy. My zMud just refuses to run more than 99 rooms ...
My mud has no code that blocks it, as there wasn't even a reboot when I upgraded. Asked friends still running older versions of zMud and they have no problems speedwalking 500+ rooms on 3-Kingdoms. (T ...