Hello Michael Webster,
Try moving the key in App_Data folder. You can check whether the key is accessed by Sitefinity from the index appended in the head meta tag of a page right after the version number of Sitefinity. If the index is "0" this means the key is not accessed.
Also make sure that the domain header is not changed due to some internal routing.
If moving the license file to App_Data does not help, could you give us the domain name for which you have a generated valid key?
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