When I was building this site I started getting the error message “Handler Could Not Be Removed” in a popup window when my home page would load.  I tried to search for a solution and didn’t find anything.  I did figure out that it was related to the gallery function on the home page.  Since I had just added a new plugin, I figured that must be the culprit.  Sure enough, when I disabled the plugin the messgae went away.  So, if you are getting that error message, it is most likely caused by a conflict with another plugin.  You will need to figure out which one it is and disable it.