I have found that Flex Builder 2 does not properly recognize any flex data services 2 mx components because it does not include the fds2.swc file by default in its install and thus cannot use the FDS2 controls.  To fix this problem, simply copy fds2.swc from <fds2 install folder>\flex_sdk_2\frameworks\libs to <flex builder 2 plug-in install folder>\Flex SDK 2\frameworks\libs.  Then you will also need to add this swc to the list of swc’s in flex builder 2 project properties under “Flex Build Path” > “Library Path”.

The symptoms of this problem are that it will not recoginize any of the dataservice mx controls in flex builder and you will see errors such as “Could not resolve <mx:DataService> to a component implementation.”