opening a file attachment from an outlook email using clickonce and a file association

I have a clickonce application (VS2010, .NET 4). I have registered a file 开发者_运维知识库association (.task), and this all works well. If I double click a file with the .task extension on the desktop the clickonce application opens and can open the file.

If I email the file however, and double click the file from within outlook, I get the open/save dialog. If I click open nothing appears to happen. If I save the file I can open it by double clicking on it.

Any ideas why the file does not open from within outlook ?

Thanks, Mark

ClickOnce applications run with no administrative privileges. The file types that you define in the deployment are not known to other applications. I'm guessing Outlook uses the same download mechanism as IE (if not the one in IE) and it just doesn't have that information available to it.