I'm using jQuery boxy plugin for Ajax modal pop up window

[AliceC]

I'm using jQuery boxy plug in for Ajax modal pop up window and and populating it through Ajax. In that window populate combo box using Ajax first time it will populate. But when I close modal window and again open it and hit the button, the combo box does not populate.I'm using php as server side language.How to fix it and where am I making a mistake?Here is the code