Recently there have been a few questions raised in the Flex Forums relating to code-hinting problems with Flex Builder. A quick search on google reveals similar issues reported on other forums and blogs.
The problem is known to occur for users of Flex Builder version 3.0.1 who are compiling with version 3.2 or later of the Flex SDK. The solution to the problem is to install the Flex Builder 3.0.2 updater available here.
The cause of the issue is a recent change to the flex-config.xml file that ships with the SDK. Both Flex Builder and the mxmlc compiler use this configuration file during compilation. The change in question is the addition of the “targetPlayerMajorVersion” token into a couple of path-elements. This token is substituted with either “9″ or “10″ depending on the Flash player version you are targetting in your build. This in turn causes the compiler to include a particular version of playerglobal.swc during compilation. Although the addition of this token did not prevent earlier versions of Flex Builder from performing builds, it did interfere with code-hinting for many of the core Flash API classes.
If you are unable to install the updater you can also fix the problem by manually removing the targetPlayerMajorVersion token from your flex-config.xml file (located in the frameworks directory) and replacing it with either “9″ or “10″ depending on your target player version.