This is the process in which we upgraded our forum from Agora to Kunena, and the issues we encountered.
As always, the first thing we did was install everything on our development server. Next, we followed the directions given by Kunena to perform the conversion from Agora to Kunena which included installing an older version (1.5.14) because the latest (1.6.3) was not compatible with the converter. That's where our first issue showed up. We could not get Kunena 1.5.14 to install. We searched Google for some answers, but found none. Somedays you win and find exactly what you need, other days you give up only to try again later.
Later came and we found a post that said to download Kunena 1.5.13 instead. We had a little trouble finding it (mostly because our frustration level was high and we didn't read the directions thoroughly) but once we did and installed it, everything fell right into place. Next, we installed the Kunena Converter and ran the process to migrate Agora. Worked like a charm. The last step was to upgrade the Kunena installed version of 1.5.13 to the latest (1.6.3) That went well too!
One day out of the blue (so we thought) all of our downloads broke. No one could access any of our downloads via the DocMan 1.5 component. After two days of server migration (actually moving our site to a different host) and troubleshooting, this is what we found:
I had forgotten two of the most helpful tools in debugging any system:
1) Error Logs and messages
2) Asking myself the question: "What was the last thing I changed?"
I have found the practice of setting the Joomla "Error Reporting" Global Configuration to "System Default" to be good. However, when I need it, I forget to change it to something more useful, like "Maximum".