When I run the installer for 3.0.5 on Windows 7, it fails due to insufficient privileges to access the default installation folder. I have already uninstalled 3.0.4. What's up?

It actually is configured that way. Unfortunately bugs in the underlying Microsoft installer technologies mean that for a small number of people, this process does not work. That's why we had to revert to advising people to uninstalling the reinstalling. But we kept the automatic upgrading flag in the installer, so for most people, running the new installer will uninstall the old software automatically.

Perhaps the occasional update failures occur because SkyDemon.exe does not have a version number (neither does Divelements.NativeSupport86.dll). The rules followed by Windows Installer in that situation are described here:

http://msdn.microsoft.com/en-us/library/windows/desktop/aa370531%28v=vs.85%29.aspx

Try adding a VERSIONINFO resource to those files.