Editing Problems.

[Describe]

Ugh! Wrong section - i put it into the game consol section.
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Heres my problem anyway:

Im trying to edit my unit, making my own following a tutorial.
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However when i go to save the coded text, it comes up the following message:

Access: to C:\program files\The creative assemblyRome-Total war\data\export_descr_unit_enums.txt was denied.
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How is it denied!? :(
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I cant seem to edit any Rome Total War Files, Help is appreciated!

And rep is given to suitable respones and facts/help. - Thanks, Joey