Can it be something in the profiles, login scripts of those 2 users, cognos.ini file or are they somehow different than the rest of the users?
I believe Citrix is not officially suppoerted by Cognos for Series 7, but i have seen it working many times though :-\
maybe this is usefull for you:
How to setup Citrix Multi-environment Configuration
How to set up a Citrix multi-environment configuration using one Cognos.ini file per single user, rather than one Cognos.ini for all users
- Create the user account, and then logon to the terminal server with that user ID. A user profile is created in the C:\WTSRV directory (C:\wtsrv\Profiles<user>)
- Logon as ‘administrator’
- Copy the customized Cognos.ini file to C:\Wtsrv\Profiles<user>\Windows\Cognos.ini.