Dear all,

I'm looking for maybe a simple solution but I can't find a proper answer.
I have a sheet where 2 to 3 persons will put their name. The first will produce a check something and put his name in column C, the second will check the same and if found correct will put his name in column D. Now I want to avoid that the same person can put his name twice as the name is putted in by a macro (it puts the login name from the pc in the cell). I guess this can be done by using validation, but I'm lost how to do this.

Can some one point me on the right track to create the validation that does not allow to same login's in column C and column D.

Thanks in advance,
megatronixs