Just to clarify: when you say server, you mean that the user can start a process with one SAS Application Server Context (like SASApp), but not another?
If that's the case, the most common issue is a permissions problem on the host. Meaning, the user may not have a host account where the app server is attempting to start the process. You should check the Object Spawner log to see if the request is coming through and then being denied for security reasons. If it is, make sure that the user has an account on this host and that if the host isn't in the default Authentication Domain, that the user has a login for this Authentication Domain in the metadata. Also make sure the user has access to the SASWORK root file system, which is required to initialize a session.
I've just taken a stab at the question, but an exact error message and/or screen shot would be helpful.
Thanks,
Tim Stearn