is this a reinstall over an existing install of the system?

when you start the sql 2005 A2ESQLSERVER instance, are you starting it with the Add2Exchange Service Account?

Did you turn off User Account Control and reboot prior to the install?

If not, then turn it off (run Regedit. Search for EnableLUA in registry and set to 0) and then reboot

If SQL Fails to install, open Regedit and search for PendingFileRename in HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Session Manager\PendingFileRename) and leave the key, but blank out the contents.  Then close and try again to open the Console.

Use these procedures to uninstall both A2E and SQL200x

http://support.diditbetter.com/kb/A2E_198.aspx

then reboot

Then Install again please.