Interested in using many of the cool new features in Flash Builder 4.6 including native extensions, I was anxious to install 4.6 and get started. I purchased CS5.5 last year and Flash Builder 4.5 came as part of that suite. I completely uninstalled Flash Builder 4.5 from my system (see below) and went to install FB 4.6. When I entered in my CS5.5 serial number the program said it was invalid and wouldn't except it. With frustration, I contacted Adobe support to ensure that I was in fact supposed to be able to install this FREE update. Which they replied that is of course was.
After searching online I found a thread in the Adobe support forums with all the answers I needed. In short, you install FB 4.6 and choose trial mode (for installs where FB was part of the suite only, see below for standalone updates) and after FB 4.6 would detect the licence and appear registered.
Note: FB 4.6 required a complete re-install of the application due to many changed included with this update. More information here.
Installation Instructions (for standalone and Creative Suite versions of Flash Builder)
Begin by uninstalling the version of Flash Builder on your computer.
On Windows, navigate to Control Panel and choose to Uninstall a program (Windows 7) or Add/Remove Programs (Windows Vista).
For Standalone installations
Find Flash Builder 4.5 in your program list and proceed to uninstall it. When given uninstall options, choose both Flash Builder 4.5 and AIR for Apple IOS Support.
For FB installed with Creative Suite
Select the Creative Suite and proceed to uninstall. The uninstallation program will now display a list of all the programs which have been installed with the Adobe suite. Select Flash Builder 4.5 and AIR for Apple IOS Support and uncheck all other programs. Continue to uninstall them from your computer.
Install Flash Builder 4.6
You may need to download the 4.6 program by going to https://www.adobe.com/cfusion/tdrc/index.cfm?product=flash_builder and choosing the appropriate version for your computer. Once you have downloaded the program continue to install it as normal. When prompted for a serial number, do the following:
Note: Some users have specified that they run into an error while installing FB 4.6 that stated:
If you get this error while installing FB 4.6, you will need to download the Adobe Cleaner which will remove additional files related to the issue. Be sure to only select the program Flash Builder before cleaning. It is also recommended by some users to completely reboot your computer after running the Adobe Cleaner and prior to installing Flash Builder 4.6
For Users who had previously installed Flash Builder 4.5 standalone
You will now need to enter the same serial number you used when you installed Flash Builder 4.5. If you have lost this or have trouble getting that serial number to work. Contact Adobe for technical support.
For Users who had previously installed Flash Builder 4.5 as part of a Creative Suite
You will now choose the trial mode and continue with the installation.
On start-up, Flash Builder 4.6 should start properly without any indication of being in trial mode as it should have now detected the previous licence used for Flash Builder 4.5.
If you continue to have issues, or the install does not work properly, contact Adobe Technical Support.