I run Debian/unstable on my desktop. Last night I upgraded the GNOME desktop environment (which I use all the time) from version 2.4 to 2.6 using synaptic, but when I restarted X and tried to login to gnome 2.6, the gnome-panel program (now version 2.6.2) gives the following error message:
I never had any problem with this using gnome 2.4. I either need help downgrading back to gnome 2.4 or help solving this problem with gnome 2.6.
Googling for this problem returned scant results, mostly other people having the same problem but I found no solutions/workarounds to fix this problem.
Any suggestions?

I remember having that problem too when I upgraded to gnome 2.6, but it disappeared when I restarted (if I remember well, not sure). If you don't want to restart, maybe you can kill all gnome-programs maybe...

I had lots of trouble upgrading, the upgrade made my desktop quite useless. I solved it by adding experimental ( deb http://ftp.nl.debian.org/debian/ experimental main ) and unstable (I use testing) to my apt-sources and updating my gnome again, and it finally worked quite well. Now I can use most programs again, but some gnome-programs are still broken unfortunately. I'm afraid that's just the pain of living on the edge...

Succes,

Sterrenkijker

Testing still has a mixture of gnome 2.4 and gnome 2.6 packages. In my mind, this make testing less stable than unstable. For instance gnome-media and gnome-utils are still at 2.4 in testing.

I rather crudely solved the problem by restoring a backup image of my root partition I had made a week before, thus wiping out gnome 2.6 (and a week's worth of changes not stored somewhere in my home directory, which were minimal, fortunately). I am happily running gnome 2.4 again, and I may try to upgrade to gnome 2.6 when they release the next upgrade.
I'll try that experimental line in my sources.list when I get a chance to play with apt some more.

Thanks for the suggestions!

Problem: Suddenly Gnome logins get the error message: "I've detected a panel already running, and will now exit". One can with a right click open a terminal and write 'killall gnome panel' then 'gnome-panel'.

What triggered this on my computer was that another user (in my case root) changed the desktop background (no joking!) and used a .png file. After either removing the file or use a .bmp the problem was solved.

Check that out.

gnome-panel-2.8.1-5.el4

I run GNOME + Debian Unstable too.. the version on *my* system is 2.18.3. Could you post your sources.list?