I got the above error message when I tried to fix a few typos in a post. Since I believe that correct spelling is important on this site, I would suggest to remove or drastically reduce this requirement. You'll have to modify some other part of the post just to fix a typo.
Editing is a vital part of community efforts to make both, questions and answers better. Therefore we allow even unregistered users to suggest edits on posts. This however means, that even it it was a tiny edit users with a higher reputation need to review and approve this edit suggestion.
To reduce the time needed to complete edit review tasks a 6 character limit was introduced network wide. This also avoids posts to prematurely turn into a Community Wiki after too many tiny edits were made.
Usually there will be a lot more which can be fixed in a post to make it better, including formatting, or adding relevant links. After we had found other issues there only will be few posts left where we can't find more than 6 characters to possibly be edited.
In these cases we can just drop a comment, or point to the question in chat to let the OP, or another user with >1000 rep (2k after a site had matured) can perform even minor edits if needed.
As soon as we reach 1k reputation (in beta) the 6 character limit will be removed with the Edit Privilege we will then have.