Unhandled exception at line 6953, column 7 in .../Scripts/jquery-ui-1.10.0.js, 0x800a138f - Microsoft JScript runtime error: Object expected

Unhandled exception at line 6953, column 7 in .../Scripts/jquery-ui-1.10.0.js, 0x800a138f - Microsoft JScript runtime error: Object expected

I am getting a bug in this function;
 
_search: function( value ) {
  this.pending++;
  this.element.addClass( "ui-autocomplete-loading" );
  this.cancelSearch = false;


      this.source( { term: value }, this._response() );
 },
 
I find that this.source == null, which causes an unhandled exception; 0x800a138f - Microsoft JScript runtime error: Object expected.
 
I am not sure how I can find out the problem so I can fix it.
I am using VS 2012 and an ASP-MVC application.