SIW2 said:
I would have a look and see if you have a file called ei.cfg in the "sources" folder - if you do, delete it.

Then you can install any Edititon from that .iso

You should be able to do that easily if you have a paid iso handler , like MagicIso, UtraIso, or PowerIso.

Otherwise, you will need to extract the contents of the. iso to the HD , delete ei.cfg, and remake an .iso.
I tried to suggest this last week as a way to use the RTM to clean install on factory OEM licensed machine, and was accused of providing a "hack" by Snuffy.

The original tutorial and top Google result for unlocking all versions in Win7 is from this very forum: Unlock ALL Versions in your Windows 7 Build 7000 ISO

The reason it is germane is because clean reinstallers like me need access to a clean copy of required version to overcome bloaty factory installs. The legal OEM license activates with a robo-call to MS, at most, since most stickers have batch keys now (overcome by reading key ahead of time with Belarc advisor and inserting it last).