[CentOS] centos 6.2 mirror no yum grouplist

hi,

I have created a 6.2 local repository in our lan and it works fine for
packages.

However, when trying to use the yum groups, I get this:

# yum grouplist
Loaded plugins: fastestmirror, security
Setting up Group Process
Loading mirror speeds from cached hostfile
Error: No group data available for configured repositories

I have tried downloading one comps.xml file (I have tried both with
http://mirror.centos.org/centos/6.2/os/i386/repodata/e9226c33fcd943a60c7a631c67895c01e61f4e62577c37e971cfe61de32239ff-c6-i386-comps.xmland
with
http://mirror.centos.org/centos/6.2/os/i386/repodata/cffddde71947e5fe5a7ce5b77b36decb71afe14b09e3160eba4b4acdd90daa9f-c6-i386-comps.xml.gz)
and rebuilding the repo with createrepo -g /path/to/xml /path/to/rpms, but
after cleaning the yum cache and remaking the cache on the client I still
have the same error.

I am obviously doing something wrong, but I do not see what. Any hints
greatly appreciated

The repos are created with mrepo, in case this is important.

Any hints greatly appreciated.
--
Groeten,
natxo