ActionScript 3.0 :: ClassPath Errors On Compiling Main FLA File

The company I work for outsourced the development of a flash project which I have now taken over. We had a handover from the developer and all was working well. However, I have moved all files onto a new machine and now I get several errors when I compile. The project is set up as follows (this isn't all the folders):
mainFolder
mainFolder-in
mainFoldersrcfolderB
mainFoldersrccases
mainFoldersrccontainerMain.fla (and Main.as)

When I compile Main.fla (all fla's are set to compile to the bin folder) I get the error -
1046: Type was not found or was not a compile-time constant: PageEvent.
Which refers to this line in the class -
protected function pageEventHandler(e:PageEvent):void

PageEvent is a class that is found in the folderB directory - mainFoldersrcfolderBevents
It is imported into the Main class -
import folderB.events.PageEvent;
3 errors appear, all the same for the 3 times the var e:PageEvent is referenced.
It seems that the main.fla/.as cannot find PageEvent class.

Another example is this:
In the directory mainFoldersrccases is a class Case1.as/fla
this class extends CaseSpaceCore which is found here - folderB.pages.cases.spaces.CaseSpaceCore; and is imported into Case1.as
When I try to compile I get the error -
1017: The definition of base class CaseSpaceCore was not found.
and then other errors about overridden methods that is cant find because it cant find the base class.

I am using Flashdevelop (if that makes a difference) as did the developer. I have tried adding the class path in the project settings to srcfolderB but this made no difference.