The "access" command is not a standard part of mIRC, so it would not send it unless you are using a script or popup that replaces the standard /channel command. Is it possible that you have scripts or popups that have been modified to use the "access" command?
If you are not sure, one way to test this would be to install a new, clean copy of mIRC in your Windows Documents folder, using the "Portable" option in the installer, and run that to see if it shows the same issue.
