I'm trying to edit an existing AS3 application (which was built using Flash Develop) in Flex Builder 3.

The application uses Base64Encoder (using "import mx.utils.Base64Encoder"). This compiles without problems in Flash Develop but trying to build it in Flex Builder 3 (Mac version) gives an error:

"Definition mx.utils:Base64Encoder could not be found"

Indeed when using code completion (ctrl + space) in flex, on "import mx.utils." only 4 utils are shown in the list.

I've tried this using the Flex 3.2.0 sdk that came with Flex Builder 3 and the Flex 3.5.0 sdk which I downloaded from the adobe website.

Does anyone know why this might be? and how I could resolve this?

Thanks.