>>How can i force the NetSpell to not submit the form, once I hit cancel?

It's strange. The "Cancel" button should not trigger any postback, submit the form....

Please test the spell button in the following example:

http://cutesoft.net/example/general.aspx

 

Here is the cancel button html code:

 

  <input class="button" id="btnCancel" onclick="closeWindow()" type="button" value="Cancel" name="btnCancel" />