Changing Window Manager in Login screen
 

I have just installed Ubuntu 12.10 and have added a number of Window managers.

The window manages are normally changed from the login screen and are selected from a menu, the last entry of which says "Select this desktop" (or something similar).

I suspect that I have too many Desktop Environments to choose from because this last menu item no longer appears with the result that I am unable to change the Window Manager.

Where is the file that specifies the current Window manager?

Every blasted issue of Ubuntu appears to store system parameters in a different place, no doubt to keep us on our toes.

This is not anything to do with lightdm, but is a recognised bug in the "unity-greeter".

The solution is to pick the desired desktop then use the tab key to step down the menu until you reach the last menu entry which will be off screen. Once there, press the space bar and, if you've done it correctly, the menu will close and the log in box appear allowing you to log in with your nominated desktop.