How to uncheck checkbox after form has been submitted

In a classic, HTML, "self-posting form," you know that (except on the initial entry into the page) you're going to be getting some POST data representing whatever's been entered on that form.  So, when and if you see that, the first thing that you must do is to process and evaluate those inputs.  I usually process these into a struct which I keep in the Session pool, merging whatever POST-variables I find with what may already be there.

The second thing that an HTML page-handler always does, whether there were any POST variables present or not, is to build the HTML necessary to render the new, updated page-image on the user's screen.  You therefore determine, each and every time, whether that <cfinput type="checkbox"> tag, which you have for whatever reason just decided to generate, should, or should not, include the keyword, checked.

The HTML you prepare will then be sent back to the user's browser and displayed there:  it is an entirely-new HTML stream that just happens to be quite similar to the last one that the browser received.  If the browser did its work well, there is no "screen flicker" and it simply appears to the user that almost nothing changed (the checkbox is now un-checked).  But in fact, every HTML stream stands alone.

<cfif form.post_red EQ "on">

     <cfset form.post_red = "off">

</cfif>

You may have to replace the "on" with a 1 and the "off" with a 0. Try it both ways and if it doesn't work post back.

Don't do whatever you are doing to check it in the first place.