List of Facebook error codes
Facebook used to have this published somewhere, but for whatever reason it was removed. But you can find the full list here:http://www.takwing.idv.hk/tech/fb_dev/faq/general/gen_10.html
There seems to be a list now for the errors.
I posted answer for the same question here: Facebook Graph API error code list
(I found the list here https://developers.facebook.com/docs/graph-api/using-graph-api/error-handling)
In case Takwing's copy ever comes down, here's another copy: http://fbdevwiki.com/wiki/Error_codes
These codes were primarily for the REST API, but they do also come up with the Graph API. Some of the Graph API calls have underlying FQL calls that return the FQL error codes. And the direct FQL queries are still part of the currently accepted API.
Update: I'm trying to keep this list up-to-date. Please feel free to make changes as you encounter new errors.