Since I looked all over the Adobe forums for help on this one and didn’t find anything, I thought I would post my solution here.

I have recently taken a dive into the world of Flex for a project at work. More specifically, I’ve been using the Flex IDE called Flex Builder 3. While doing lots of research, I found an open-source component that looked really promising so I grabbed the code only to find that it wasn’t working in Flex Builder 3.

I’m pretty sure it was mentioned somewhere in the documentation for the component, but I missed where it said that it required Flex 4. I didn’t really know anything about Flex 4 (also called “Gumbo”) so I researched and found that it was a pretty sizable overhaul (for someone like me who is just starting to learn Flex at version 3) and that the new IDE for it was still in beta, potentially going to be released soon. So I thought what the heck, I’ll get the beta. Then the trouble began.

I fired up the Mac installer. I clicked through all the things you normally click through without paying much attention but I got stopped at a message saying I needed to close all browsers. Ok, no problem, I thought. I quit Firefox and Safari, and even Thunderbird just for good measure.

No dice. The message popped up again immediately. I thought maybe I had gotten a corrupt download, so I tried to get the file again. Mounted it, and still had the problem. I did some searches to see if anyone else was having issues and came up with nothing similar.

“Ok,” I thought, “I’ll just reboot in case leftover processes or anything are causing trouble.” This would have to fix it, right? Wrong. After rebooting and not starting any programs, it STILL wouldn’t install. By this time, I was not a very happy camper, having sunk a sizable chunk of time into getting this program running.

I finally decided to check my startup items in System Preferences > Accounts > Login items. I saw that my Xmarks for Safari plugin was running at startup. Aha! Not wanting to take any chances, I removed it completely instead of just un-checking the box for it. I rebooted one more time and Voila! It FINALLY installed.

So kids, the moral of the story is: check those startup items! Even a seemingly innocuous thing like a browser plugin can prevent you from installing programs.