Setting file type icon

I want one the files I install to have the application icon.
I think l have done it correctly, as on my PC it is OK but a user says it is not correct on his computer.
I thought I just need to go into file extensions - specify the file extension and the file extension properties set the Extension, ID, ID description, and file - thich is the executable with the icon.
Is there something I have missed?

Assuming the path to the .exe is correct, I think the icon you would like to be displayed is not the first icon in the file resource. So you have to specify the correct "Icon Index". Or make sure the icon to be displayed is the first icon in the .exe resource (this requires a recompile of your .exe).

Hope this helps.

Friedrich