I've just started working with the G.E.C.K. I'm trying to go through Bethesda's initial vault tutorial.

I did the up to the part where you create the small hallway with stairs and doors.
/gamesas_Tutorial_Layout#Making_a_Hallway

Everything was going fine so I decided to test out my mod by traveling to the cell using the COC command. I placed the COCMarker in the cell (in a valid location - inside a door), made sure the mod was active in the launcher, started the game, typed in COC Vault74a and...nothing. The COC command isn't working. Instead of transporting me to the new cell, the game just stays where it is.

I noticed that my new cell has an asterisk in the editor ID. Instead of 'Vault74a' it's called 'Vault74a *' The cell I duplicated from, Vault108a, also has an asterisk. I can't get rid of this asterisk in the name and that's what I thought was making this not work. At least I thought that until loading up the sample file from Bethesda which worked fine, the COC command did what it was supposed to, even though their Vault74a and Vault108a cells still had an asterisk in their names.

By now the only possible thing I can think of is that since I have doors that open to nothingness, I.E. I didn't finish the entire layout, that for some reason the game won't let me visit the cell. That seems dumb but the only explanation I can think of.

Any insight into why I can't use COC to travel to my newly created cell?

The asterisk simply identifies the cell as something new to your mod. If you create any new item, be it an NPC, clutter item or cell, the GECK will put an asterisk next to the name so that you can see that it is something that belongs specifically to that .esp/.esm.

That asterisk should be next to the name of your cell. From what you say, it looks like there's a space in there - i.e. you have accidentally typed a space character on to the end of the name of your cell. Try renaming it, making sure to avoid putting any spaces in the name.

I don't think a space is the problem. The editorID of the cell indeed has a space then asterisk, but I cannot get rid of the space. If I try deleting the space and asterisk, it just puts them back.

So I understand that the asterisk just means the cell is new to the mod. What I'm really wanting answered is why I can't COC to the new cell. When I put in the command at the console it just goes back to the game as if that cell didn't even exist. I definitely have the mod enabled so how come my custom cells aren't getting put in the game?

P.S. I tried just duplicating a cell and not modifying it at all but I can't even COC to that cell - so I don't think it's a problem of not having some requisite object in the cell.

Did you try to enter your cell in another way ? Place a xmarker "mycellmarker" where you want the player to appear and in console type player.moveto mycellmarker.
See if it works. Perhaps it has something to do with your cell, there is no reason for COC not working.

I placed an xmarker but it still didn't work. It's as if the cell I created isn't even in the game.

Can you COC to a cell in the base game?

make sure the COC marker is a persistent reference, and make sure its not a duplicate of some other coc marker. also make sure there is only one coc maker in your cell. also triple check all the names and spelling that you use.

i dont know if it matters, but make sure the fast travel option isnt on or off and preventing you somehow.