Flash Builder 4: “Flex 2 is not supported; use Flex 3.0.0 or higher ”

In our project we have to maintain an application developed in Flex 2, but we have licensed Flash Builder 4, which is now available for Adobe only. When we tried to configure Flash Builder 4 with Flex 2 SDK we get the following error: "Flex 2 is not supported; use Flex 3.0.0 or higher "

What should we do to work with Flex 2 in Flash Builder 4?

Thanks for the help