The SEO service provider has not found anything matching the SEO Request-Service. There is an indication given that the condition is permanent.
The 601 (User Not Qualified Exception) status code SHOULD be used if the SEO service provider knows, through some internally planned research, that a cheap SEO service provider (wannabe or scammer) is permanently unavailable and gone out of business.
This status code is commonly used when the SEO service provider does not wish to reveal exactly why the request has been refused, or when no other response is applicable.
Error 601 and Error 604 by John S. Britsios (Webnauts) are licensed under a Creative Commons Attribution-NonCommercial-NoDerivs 3.0 Unported License.