The Complete SEO Guide to HTTP 5XX Server ErrorsAs a website owner or SEO, you may have encountered a 5XX server error at some point—you may even be seeing this error message on your screen right now. This is a simplified but comprehensive SEO guide to the most common HTTP 5XX server errors, their causes, and how to troubleshoot them. Each 5xx server error varies widely within its class, and these server errors can occur on different levels. The Most Common 5xx Errors:The most common 5xx error. The most common 5xx server errors can be frustrating to deal with, so I made a guide on each one—which is all linked in this post.