This error occurs in the TkI Scan menu. If it's not a hardware problem, it may be due to the fact that the timer is declared to run in preset mode (software) but from the hardware side it is operated as a normal timer. Remember, if a timer is operated in preset mode, it opens that gate until it receives a certain number of counts, from a monitor counter. Normal timer operation means that the gate is opened for a selected time.
User Action: Enter the Scan-Options-Select_Scan_Devices menu
and make sure that the timer is not in preset mode.
Then stop the timer by issuing a * = stop_timer(tXX)
command. Replace tXX with the corresponding timer name.