Flex 4 main class interface errors

I ended up a few times with these kind of errors while migrating to newer Flex 4 builds:

Description Resource Path Location Type
1044: Interface method invalidateParentSizeAndDisplayList in namespace mx.managers:ISystemManager not implemented by class _Main_mx_managers_SystemManager. example-project line 23 Flex Problem

Description Resource Path Location Type
1144: Interface method callInContext in namespace mx.core:IFlexModuleFactory is implemented with an incompatible signature in class _Main_mx_managers_SystemManager. example-project line 23 Flex Problem

The location/resource for these errors is the main MXML itself but that’s all you get. So you ask yourself what went wrong? A quick Google search does not help (until I blogged this hopefully) so where to start?

The problem is that you are mixing different SDK versions. In my case my project linked to a library which was compiled with a different SDK version and now the important thing: the framework linkage in the library was set to “Merge into code“. Change it to “Use default (external)” and you are fine.

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5 comments to Flex 4 main class interface errors

  • Anon

    I just opened up a project I had been working on for a while and my environment decided to lose it’s mind and throw the 1144 error. I’m on a super tight deadline and this is the sort of thing that just makes your heart stop. Google brought me to you and it solved it. Don’t usually post these, but I figured I owed you a “thanks for saving my @$$”. Keep blogging. We need you. :)

  • Tim

    Thank you, I got the same error and was really concerned how to fix it.

  • Bogdan


    This did not work for me :(

  • Nick DeLong

    Thanks! For anyone still having this issue, it is exactly as described above, but the solution proposed here may not work in every case.

    In my case, I had a SWC project that was compiled with a different version of flex (4.5), and it was in the library path for a project that I was trying to compile in flex 4.1. The solution was to recompile the imported project with flex 4.1.

    Thanks for posting this!

  • Andrea


    I searched the reason for this for days and neither Adobe mentioned anything!
    Thank you!