After adding Flex 3.0 compiler folder structure to project(replacing existing incompatible LCDS 2.5.1).
But facing new problem:
Warning: 'getString' has been deprecated since 3.0. Please use 'ResourceManager.getString()'.
And ResourceManager.getString() is not present :-(
Instead, I have tried out with ResourceManager.getInstance().getString("resourceBundle", "propertyName");
This solution has removed warning, but failed to load property data :-(