Problem with PC.
25 Khz I think is correct.
I had the error message come up because XP was making the PC busy when Mach3 started.
Make sure no rogue programs are running.
When Mach3 starts it enables it's driver, and at this moment the PC must be healthy and not busy.
Mine is connected to a network, and every so often it goes off into the weeds at the wrong time. Restart Mach3.
Use Ctrl-Alt-Del to see what else is running.
Super X3. 3600rpm. Sheridan 6"x24" Lathe + more. Three ways to fix things: The right way, the other way, and maybe your way, which is possibly a faster wrong way.