Was finishing the wordpress plugin partially coded by my team member and while trying to submit it as POST twenty twelve theme said:
This is somewhat embarrassing, isn’t it?
Well honestly speaking, yes it was, coz after trying few different things (including removing the plugin completely) it still gave this error. (You can refresh the page with 404 error – resubmitting the values POST be the contact plugin – even after deleting it)
Anyway, lets come to the point, the solution was pretty simple.
The issue was that he used wordpress specific value in the form. He was “name” field in the form which caused this error.
So the solution to the contact form showing 404 error was to change the “name” field in the form to something else!