I don't know if this is because it is an AS3 project and not an MXML project but I'm running into this error when I try to use the ArrayUtil class:
1202: Access of undefined property ArrayUtil in package mx.utils. Is this class not available in an AS project? An really the code complete for that package is only finding 2 classes: NameUtil and StringUtil I can work around it but I'm worried about missing so much of the mx.utils class.