There is THIS question and I wanted to edit it to make it clearer and also add the image inline but I can't. The edit button is grayed out. I have seen this once before and I wanted to know why some questions can't be edited.
There are a handful of conditions where we will stop accepting suggested edits:
A large number of suggested edits by you were rejected in the past week (at least 5 more than one-third of your accepted edits).
We are out of empty slots in the queue (currently 20 120 200)
There is an edit to a particular post that was not approved yet.
You are not logged in and the post is less than 10 minutes old.
You are on a child meta.
In the past no "edit" link would be shown at all; since July 2012 the edit link is disabled and the mouse hover tooltip will explain why an edit cannot be suggested, like "Account is not allowed to suggest edits".
See this meta for full info.