When you install Titanium Developer and decide to upgrade to a new version, chances are you will encounter a network error problem that persists rendering the application unusable because whenever you start the program, it will try to resume the upgrade installation. You can override the upgrade by deleting the folders according to the two operating systems that this application is available in: Windows and Mac OS.
For Windows, you can delete the folder Titanium in C:\Documents and Settings\[USER]\Application Data\ where [USER] can be your user account or choose the “All Users”. If there is a Titanium folder there, delete it.
In the case of Mac OS, I just go to the folder /Libary/Application Support/Titanium. The files are all there. If you want no hassles, just delete the folder right away. That should solve that network error and you can then use Titanium Developer.