This question is probably better asked it the Flash Builder forum.
However, my guess is that in the beta the installed SDK was called "Flex Hero" and in compiler settings for your project its set to that sdk still, even though it doesnt exist.
Try right clicking on your project and opening the project menu. In the Flex Compiler section select the radio button for "Use a specific sdk" and then from the drop down choose 4.5 or 4.5.1 ( i am not sure which one you'll have)
See if that gets you around your error.
HTH
sim