The Gnome Buildbot has been showing many modules failing on update stage for some time. This had to do with some changes in Jhbuild to support Mercurial repositories (back in May) and, specially, the inclusion of mercurial repositories in the modulesets.
The reason for this to fail in the Gnome Buildbot was that we were not using an up-to-date Jhbuild version and a simple update would not do the trick here because we were using a slightly patched Jhbuild version. You might wonder why we did not push our patches into jhbuild in the first place, but the truth is that we did it since the very beginning, however, there was still one of them pending to be applied because it needed some tweaks prior to go upstream and these fixes were postponed for too long… (my fault).
When the modulesets were updated to actually include mercurial repositories, our jhbuild version raised the problem because it did not know anything about this repository type. Nothing better than actually see a problem to start working on solving it, suddenly fixing that pending patch became my most important ToDo item :), after some days of work and the valuable help of Frederic Peters, we managed to get a functional, corrected and up-to-date patch against Jhbuild trunk, so finally the Gnome Buildbot is working using a non-patched version of Jhbuild.
For the future, now that we run a non patched version of Jhbuild, and taking into account that jhbuild is a key component of the Gnome Buildbot, we should consider a regular update mechanism that keeps our build environment up-to-date.
BTW, thanks to Frederic for helping us with this! (and also with the other patches we merged in Jhbuild), you have definitely made our life much easier :).