x-window manager does not run after upgrade

I have a weird problem which came about after the latest upgrade of X (I'm running debian unstable all the way). X starts correctly, I get the xdm dialogue, but when I log in with username and password, I get the grey grid for something like 10-30 seconds, then back to the xdm login dialog. How

x-window manager does not run after upgrade

I have a weird problem which came about after the latest upgrade of X (I'm running debian unstable all the way). X starts correctly, I get the xdm dialogue, but when I log in with username and password, I get the grey grid for something like 10-30 seconds, then back to the xdm login dialog. Ho