Google Adsense is currently experiencing an issue with Western Union sign-ups. Essentially, whenever a publisher selects Western Union as their payment method, they will be prompted to update their state code to a state code that matches the list of Mexican state codes accepted by Western Union. If your country of residence is not Mexico, you cannot update your state code to a Mexican state code, and thus cannot sign up.

Google Adsense engineers are working to resolve this as quickly as possible, and is expected to be resolved by 8th April 2011.