Webform submissions limit. "ajax.module: An unknown error has occurred" error thrown when reached

Hi, I found a bug on ajax.module's related to limiting user submissions on a webform.

if you "Limit the number of submissions a user may send within a specified time period" on a webform to, by example 3, when you reach that limit, ajax.module throws a "ajax.module: An unknown error has occurred." alert instead of the "You may not submit another entry at this time" message.

On firebug, you can see the expected message. Go to console tab, then expand the request and finally select HTML tab. That's exactly the problem: ajax.module is expecting JSON and is getting HTML.

I'd tried to figure out how to fix this, but I had no luck, so I am here posting this issue.

I you have a clue on how to fix this, please tell me.