Flex Error

Okay so I’m decently proficient at AS3 so when I tried switching to to Flash Builder (Flex) I got confused fast. I’m following this tutorial here

I’m getting this error, which I believe is being caused by a problem with the app.xml file but I can’t really understand the error.

Please correct the following problem in the app.xml file for this application.

invalid application descriptor: descriptor version does not match runtime version
Launch command details: “C:\Program Files (x86)\Adobe\Adobe Flash Builder 4\sdks\4.0.0\bin\adl.exe” -runtime “C:\Program Files (x86)\Adobe\Adobe Flash Builder 4\sdks\4.0.0\runtimes\air\win” “D:\Documents\Documents (spencer)\AdobeScripts\FacebookUserStatusAIR_1\bin-debug\FacebookUserStatusAIR-app.xml” “D:\Documents\Documents (spencer)\AdobeScripts\FacebookUserStatusAIR_1\bin-debug”

Please help,