- The most obvious reason for this error is that the method you called does not exist in the webservice you called. This could happen due to a mistyped method name (e.g. GetAccountInfo instead of getAccountInfo) in your SOAP request. This could also happen because you sent your SOAP request to the wrong web service.
- You could also get this error if you mentioned a wrong namespace against your method. For example, For example, the following call to https://adwords.google.com/api/adwords/v12/AccountService will cause the error:
Link - from AdWords API Blog
Related: Now Available: AdWords API Local Database Sync New website: Facts about our Yahoo! ad deal