Yesterday we released Flex SDK 3.5a, an update to Flex SDK 3.5. This is from the Flex Team blog:
The Flex team has released an update to the 3.5 SDK that addresses an issue with the Flex-based AIR auto-update UI packaged within the SDK (SDK-24766). The refreshed build, SDK 3.5a, has only a few files modified in order to fix this issue and this change does not affect the signing and caching of the SDK 3.5 RSLs originally released in December.
We encourage all developers using SDK 3.5 to upgrade their build to SDK 3.5a to continue their development. The SDK 3.5a can be found in the “Latest Milestone Release Build” table here: http://opensource.adobe.com/wiki/display/flexsdk/Download+Flex+3.
Basically, this release fixes a bug related to the Update Framework: ApplicationUpdaterUI no longer works in Flex 3.5.