Hi Hurricane,
Yes we encrypt the credentials for google analytics using the same encryption as is used for passwords, so after changing the key it cannot decrypt it. You can fix it by first clearing the values from the db like this:
UPDATE mp_SiteSettingsEx
SET KeyValue = ''
WHERE KeyName = 'GoogleAnalyticsEmail'
UPDATE mp_SiteSettingsEx
SET KeyValue = ''
WHERE KeyName = 'GoogleAnalyticsPassword'
If there is more than one site you should add AND SiteID = x to the where clause of each statement, replacing x with your site id.
then touch Web.config to clear the cache, then re-configure your analytics account settings so it will encrypt them with the new machine key.
Hope it helps,
Joe