Could be a known issue. Did you changed the windows domain of the database server after the installation of the informix software. If this is the case then you are runinng in a known problem, just re-install the informix software and the problem is gone. If you renamed the server then this also happens sometimes. There is a utility availiable somewhere to change the computername withing Informix. I only don't exactly where it is. My advice just re-install, it will only cost you 30 minutes. Be sure to save you configuration files etc.
Please let me know if this was/fixed the problem.
Greetings,
Rob Prop