In the post you refer to it states that reinstalling ALL the applications (not just FM and RH) fixed the problem. I'm not sure if this is the case with your scenario or whether the applications were bought in isolation.
Thank you for your reply, RoboColum(n). It turns out that the solution was to use DITA-OT 1.5 rather than 1.6.3. I was mistaken when I said above that my colleague and I had the same setup. He has been running the OT 1.5 for quite some time and since I recently installed it, I went for the newer version.
We can use version 1.5 for what we need, but it is rather strange that version 1.6 does not work to import ditamaps in RoboHelp. The information I found states that version 1.6 improves performance, provides clearer error messages and has undergone significant code cleanup.
I would be interested to know if Adobe will be keeping up with future versions of the DITA Open Toolkit. There are plans to incorporate the creation of context-sensitive webhelp in a future version, which would be really helpful for us.
Thanks for posting back Heather. It will certainly help others in the future. I can ask around about DITA 1.6.3 and will post back if I hear anything useful.
I hope I can spare others some frustration through my experience.
I would appreciate you doing some asking. Thanks.