tag history problems

[vvl]

I found the "latest" tag "PROJ_3" with command:

cvs -d $CVSROOT history -T -a

but "checkout" command for this tag:
cvs -d $CVSROOT co -r PROJ_3 <working_dir>

returns error: "no such tag in repository". 
Any idea what I do wrong here?
Also, what would be command to get tag history for the certain module
in repository?
cvs -d $CVSROOT history -T -m <my module> -a doesn't work.

And how can get list of modules in repository anyway?

Your help would be really appreciated...
Frustrated CVS newcomer.