Informix 9.4 Arcserve 11 Unable to open connection to database server

We're running Informix 9.4 on Windows 2000 Server (sp4) with Arcserve 11 Backup Agent for Informix. These two pieces of software are installed on a "clean" machine (flattened and rebuilt). Just after the Informix 9.4 software and the Arcserve agent was installed, I ran a full backup from the Arcserve Manager server. It worked just fine. The DBA started tweaking the Informix server to get it ready to import the data from our production database and now it won't allow us to back it up any more. We get the Unable to open connection to database server 155 (0x9b) error. I have another clean system that I installed a similar configuration on and it has continued to allow us to use Arcserve to back up the database (no changes were made to the Informix server configuration though). A couple of other notes - the Arcserve manager resides on a separate server and all of the servers in my configuration are workgroup (not domain) servers. We've compared the configurations of the two servers mentioned above and re-entered configuration data until we're blue in the face. About the only thing we haven't done is uninstalled and/or re-installed any of the software. Anyone have any ideas about what might be causing this problem? Thanks, Rochelle