It seems the Galactic Court For Name Conflict Resolution needs to open a branch for individuals (not just races, civilizations, and worlds). Either the writers forgot, forgot to check, or somehow didn't know a name was already in use....

It might work if two characters with the same name are of different generations (they could be related); otherwise, well:

It first appeared that Tuvok might have been married to Ambassador T'Pel, the Romulan Subcommander Selok who posed as a Vulcan, in an attempt to infiltrate the Federation ("Data's Day" (TNG)). That would have been an interesting story. Perhaps Selok was falsely using the name of Tuvok's wife as the deception. This would actually work if they make the real T'Pel ("Persistence Of Vision" (VOY)) an ambassador. Granted, someone in the Federation Diplomatic Corps would have had to be really sloppy not to notice that the real T'Pel and fake T'Pel don't look anything alike.

There's Crewman Dax (Star Trek VI) and the Dax symbiont (DS9). It would have been a nice bit of continuity if this had been one of Dax's earlier hosts, but Crewman Dax wasn't a Trill.

Kes (VOY) and the Kes people ("Attached" (TNG)).

Galen ("The Chase" (TNG)) and Galen (Picard's fake identity) ("Gambit, Parts 1 & 2" (TNG)), but this may have been done on purpose.

The Galen thing was done on the purpose - if anyone were checking Picard's credentials while posing as Galen they would find he would be an archaeological expert.

Go to my T-K ruminations on the Klingon board in the Classic Trek Sink and the new topic on the Jedi`s Sink.

well, there is the M-5 computer from "the ultimate computer", and the M-5 robot from "requiem for methuselah".

Chakotay - similar to Jekote (exact pronunciation)

Dr. Soran and Soren from TNG's 5th season

And from Phil's book

Khan Noonian Singh - Dr. Noonian Soong

There was an Admiral Chekote (same pronunciation) on DS9.

The Noonien Singh/Soong thing was something Roddenberry himself was responsible for IIRC. It seems he had a buddy years ago by that name and he was trying to track the guy down.
Similar names:
Kirk- our famous captain
Kirok- Capt. Kirk's alter ego after a bump on the head
Kurok- A Klingon from Unimatrix Zero.
Kira- our favorite fiesty Bajoran freedom fighter.
Also, there were two Gul Torans and a Bajoran named Toran. Duras' illegitimate son was named Toral.

Annorax from VOY's Year of Hell: compare his name to that given to the many obsessives who would lay down their lives for the show.

(I'm fired.)

Don't forget the whole Gul Toran thing in DS9...