Question

Couldn’t be because of browser differences. I have tested in Chrome aswell. Could it be an error in my code? When I press the check box, the textbox is suppose to be disabled. this doesn’t have so far. Here is the code I have:
I put the script on the top of the section of the page.

Form name : frmPost

 <script type="text/javascript">
      function enabledisable() {
                if (document.getElementById("ePrice").checked) {    
                    document.frmPost.txtPrice.disabled=false;
                } else {
                    document.frmPost.txtPrice.disabled=true;
                }
            }​
    </script>

<input type="text" name="txtPrice" id="txtPrice" size="5">
<input type="checkbox" id="ePrice" name="ePrice"  onclick="enabledisable()"/>

Answer 1

Checked it on IE9, Chrome and Firefox

 <script type="text/javascript">
      function enabledisable() {
                if (document.getElementById("ePrice").checked) {    
                    document.frmPost.txtPrice.disabled=false;
                } else {
                    document.frmPost.txtPrice.disabled=true;
                }
            }
    </script>
<form name="frmPost">
<input type="text" name="txtPrice" id="txtPrice" size="5" disabled="disabled">
<input type="checkbox" id="ePrice" name="ePrice"  onclick="enabledisable()"/>
</form>

All is ok. Are you sure, that your form is named as frmPost?
And I believe that input txtPrice should be disabled by default