Hun in the Sun Campaign problems

[huninthesun]

I can replicate that problem (campaign is listed in the Campaigns menu but nothing happens when you click on it) if the RAFCampaign.dll file is missing. There are two DLLs that should be in the steamapps\common\il-2 sturmovik cliffs of dover\parts\huninthesun folder - RafCampaign.dll and RafCampaignMission.dll. They can be found in the "campaign-parts" section of the installation file.
You may have just copied the folders from "campaign-parts" and missed out the dlls?