Mine did that as well when I updated the firmware of my Power Commander. Doesn't allow you to use cruise control. I haven't updated the firmware to the October 2011 release yet to see if it fixes mine. One can only hope it will.
Had this happen twice with mine have a PCV and if the 6 Goes out, So does Cruise, but both times it happened after stopping and starting back up again no more problems .. Been at least 6 months now since done it .. Now that posted this will probably do it again ..
My 6th gear light and Cruise Control became erratic after installing a PCV. The cure is to go into the Power Commander with a laptop, go to the Power Commander Tools Menu, click on To Configure Harley ECM Data. There will be a check box to the left of Diagnostic Port Enabled. Uncheck the box. Click OK to accept the change. Worked for me.