Im having the same issue, Ive tried to put the file in the directory with no luck. Which mod in the mod depot is supposed to have the ctab contained in it?
The 506th pack is supposed to have the Ctab userconfig in it, but it was uploaded without one. CPT Drumheller added it onto the Recruit Mod Depot a couple weeks ago. It's at the bottom of the list of required mods.
Have you created a folder called userconfig under the Arma 3 directory?
That's where you'd either merge the userconfig that CPL Wischuf uploaded onto this thread or just grab the ctab folder from his userconfig and drop it into your own userconfig. Otherwise, you can just download the one CPT Drumheller linked on the Recruit Mod Depot that I mentioned earlier.