hm, let's check this anyway-
to get a list of installed skins:
replace skin1 with desired etc:
zmprov gcf zimbraInstalledSkin
Yes, you have to type zimbraInstalledSkin between each.
zmprov mcf zimbraInstalledSkin skin1 zimbraInstalledSkin skin2 ...
(You could always do +/- instead but all at once can't hurt.)
Do a tomcat stop/start. (or if you want a full zmcontrol stop/start)
Then go through your user/cos theme settings.
Clear your browser cache and try the ajax or lite web-client still listed there?