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".