I have spent several hours spinning my wheels with the following problem. Within the same Workspace my pre-existing projects continue to work. However, I purchased a small project from ActiveDen.net and it is throwing the following error. I have installed and re-installed the Flash Player to the latest debug version without anything being resolved. How the hell can this possible, within the same workspace?
Flash Builder cannot locate the required version of Adobe Flash Player. You might need to install the Flash Player or reinstall Flash Builder.
Do you want to try to run your application with the current version?
Yeah, I had that problem, too.. Sorry to say I can't remember how I fixed it, but I think it was a combination of cleaning/recompiling all projects and restarting FB and/or the PC.
I did not install any new player etc.
However, if you want to try that, here is a link
http://blog.ysatech.com/post/2009/07/31/Flex-Builder-cannot-locate-the-required-version-of -the-Flash-Player-You-might-need-to-install-Flash-Player-9-or-reinstall-Flex-Builder-Do-yo u-want-to-try-to-run-your-application-with-the-current-version.aspx