Hi i had experienced the same kind of problem but the error code was not the same,
it was :
ERROR_CREATE_FAILED 1631 The Windows Installer service failed to start. Contact your support personnel.
can you do a verbose loging to chek your error code, because there is no 2103 error code in the windows installer doc
the raison of this problem was the windows installer service NEED a hkcu registry hive to be loaded because it MUST check if there is somme user policies.
If you try to launch windows installer from a service witch dont load the profile for the acount it's logged on with,the windows installer service will fail to load
to be sure that it is the raison of your problem,
try to configure the service loggin account to be the same as the one of the interactive user.
if it work thats mean you can resolve the things by writting a profile loader utility, or try to get the beforemsi.exe utility from tivoli support