I have found this thread:
Login Manager Problem
I am running into the same problem that brandsavvy is. Several sites have installed without any problems. Just one of my sites sometimes will - most times won’t let you log in.
Just wanted to check if anyone has had any luck finding a resolution - or if there is something I can communicate to my Rackspace folks?
[*EDIT*]
It never fails search and search... ask for help and the answer pops up. This might be a good thread to bookmark if anyone is on the RS Cloud Environment:
http://modxcms.com/forums/index.php?topic=35112.0
