Informix Perl DBI/ESQL/Online problem

I am trying to install the Informix DBI drivers for Perl onto our AIX 4.3.3 machine where we are running a very old Informix OnLine 5.10.UC1. I have downloaded the DBD-Informix-2005.01 package and it requires ESQL/C, which it suggests can be sourced as part of the Informix Client SDK (Version 2.81) which I have installed. The problem is, I can't get the ESQL/C to make a successful connection into the Informix databases. It keeps telling me I do not have permission which suggests a missing hosts.equiv entry, although I do have every name I can think of in here. Both the client and server are the same machine, so I would have hoped it was going to be straight forward. I'm left wondering if there is just version incompatibility, as one of the README files for the SDK says that the lowest tested Informix version is "Informix Dynamic Server 5.20.XX". The sqlhosts entry we are trying is : labserver onsoctcp labserver sqlexec The hosts.equiv entries are : labserver labserver.medlab.co.nz medlabh medlabh.medlab.co.nz localhost localhost.medlab.co.nz Each of these machine names exist in our hosts file. Any help anyone can offer would be appreciated. Stu