You have some form of line noise that the speech engine is, 'hearing' as a command. The closest match before was, 'thanks' but now the closest match is, 'mark'. This is really outside of VoiceAttack's control, as it's going to boil down to either a hardware or driver issue on your system.
Some things you can try:
-Update your sound drivers. This is a culprit a lot of times.
-Try a different mic. A quality usb headset is recommended.
-Crank up your confidence level to try to get around the problem. The global confidence setting is on the options screen, however, if you have a command (such as, 'mark') you can set the confidence level there to a higher value. Also, if your command weight on the options screen is set high (above 75), VA will attempt to make a, 'best guess' as to what you are saying... if it's high enough, a cough will result in a command execution.
Hope that helps!