Diane
I have limited experience with the 3005 concentrator. But with other 3000 concentrators that I have worked with you can configure the logging level for the various reports. It sounds like your logging level is set to not provide much detail (and minimize volitility of the log file). Perhaps you can experiment with changing the logging level (higher numbers represent more detail) and see if you get more of what you are looking for.
Having said that I am not sure that the concentrator log messages (at any level) are goig to be very helpful about why webmail did not work. And my experience is that even at greater level of detail they are not real helpful about why an individual user got disconnected.
Good luck.
HTH
Rick
HTH
Rick