Often we face issues in plugins and get error codes from CRM while debugging our server side code.

For e.g.

Error code 80048531 means CustomImageAttributeOnlyAllowedOnCustomEntity which is

A custom image attribute can only be added to a custom entity.

Just happened to pass by a cool resource containing the error codes and their descriptions. It is available on following path in CRM 2013 SDK:

SDK\SampleCode\CS\HelperCode

has excel named CrmErrors

Refer to image below:

Hope it helps!