Sorry, I seem to be missing the concept. Using LocalizeControlTitle like I did above:
Localization.LocalizeControlTitle("ControlTitle", LocalResourceFile, "Edit")
Where ControlTitle = "ControlTitle", ControlSrc = LocalResourceFile, and Key = "Edit"
I changed the entry in my resource file to add the Key as you stated like so:
<data name="ControlTitle_Edit.Text">
<value>PAGE TITLE</value>
</data>
I still get the error. Am I calling it from the correct place (PageLoad event)?