My company bought CS 5 for me in April, and I installed the trial of FB 4.5 because it had such great productivity enhancements and I knew the free upgrade was coming. I uninstalled the trial and installed CS 5.5. When I launched FB 4.5, my project was full of errors, where FB doesn't recognize basic data types such as int, DisplayObjectContainer, etc. How do I tell FB where these Classes are? I am completely dead in the water until this is resolved.
OK, I managed to figure it out and resolve it. For those who might encounter this problem...
I started the project in FB 4, so when I installed the trial of 4.5, I just pointed the project to the 4.1 folder (because the 4.5 SDK caused some issues in my project). When I uninstalled 4, the SDK was also removed.
The solution was to download the 4.1 SDK to the 4.5 folder, then point to that. I had an issue in that 4.1 was the default SDK, and I had a hard time getting the "Configure SDK's" dialog to open (it kept failing with an "invalid values" message. I finally found that clicking "specific SDK" allowed me to open the dialog.
Hope this helps someone else.