It sounds like either a duplicate PC or a problem with the rogue sensor. And seeing your update it screams that its a duplicate.
It might be worth Deleting the sensor data from the particular sensor (through looking at the rogue sensor details) and allow it to re-scan. This will provide you with a fresh set of data.
If this machine still shows as a rogue i would check your network for a duplicate machine name. If it doesnt then its just the sensor keeping maybe old information.
Will be interested to hear how you get on.
More digging has resulted in finding out that McAfee is ignoring a Teamed network card and is reporting on the indivdual cards.
Hence two macs and one IP address! can't locate an option to merge the two, so will have to add it to my ignore list unless any one comes up with another option?
Have you changed Detected System definitions settings under Server configuration.
Manue|Server Configuration|System Defication Settings|See rough system settings change them to point epo not to decet rough system.
Edit option is at the bottom of page.