I edited your post to include this bit for your initial issue, which was that the server was not configured to support the amount of variables that where being generated for the amount of forums that you had configured (30 permissions * total forums) as the value was the default (1000, which would max out at 30 forums).
Moderator Edit: Issue was caused by a low PHP max_input_vars value for the amount of forums on the users install (30*totalforums=lowest value); issue was fixed by increasing the value at the host level.
