The multimeter is auto ranging and i've got it set to mV. After the first round of error messages, we took the power tubes out, cleaned the sockets with electrical contact cleaner, then put the tubes back into different sockets than we originally tried but still got the error...The multimeter doesnt seem to have a problem reading anything else other than the left bias test point on this darn amp! BTW the tubes are brand new JJ EL34's...