Something in the installation process for Beta 3 has messed with the settings in the Registry key HKEY_CURRENT_USER\Software\Logos4. The "InstallDirectory" value was removed in addition to resetting the Logging sub-key and removing the other sub-keys. I'm not sure of the extent of the damage, but people who had originally installed in a non-standard folder will be experiencing problems (and you probably know about that already from other threads).
For the majority of us, though, the main issue is that diagnostic logging has been turned off if we had it enabled before. It's a good idea if you're beta testing to run with it enabled all the time, so that a log file will be generated in case Logos should crash or you have some other difficult to diagnose bug to report.
Here's how to re-enable logging (or enable it for the first time if you haven't been running with it turned on):
http://wiki.logos.com/Diagnostic_Logging
