The Prompt on combo box is not disappearing after a value is selected.

Question

Hi guys,
I am putting in the prompt "Course Category" which starts off black and when a value is selected it turns grey but doesn't disappear, obscuring the selected value.
I have tried putting in the line course_step1.prompt = ""; in the post selection part of the code but this has no effect.
Interestingly when I test just this scene and not the whole movie this problem dosen't occure.
This is a quote from my code I hope it gives you the idea...
Thanks in advance,
var course_step1:ComboBox = new ComboBox;
                sophia_page2.addChild (course_step1);
                course_step1.x = 245;
                course_step1.y = 12;
                course_step1.width = 200;
                course_step1.dropdownWidth = 300;
                course_step1.prompt = "Course Category";
                course_step1.dataProvider = new DataProvider(cat_array);
                course_step1.addEventListener(Event.CHANGE,select_cat);
                function select_cat(event:Event):void
                                var cat_select:String =(course_step1.selectedItem.data);
                                course_inst1.textColor = 0x999999;
                                course_inst2.textColor = 0x000000;  
                                course_inst3.textColor = 0xCBDEF5;
                                course_step1.prompt = "";
                                //trace ("http://onedev/one/Sophia/CourseQuery2.asp?Cat=" + cat_select);
                                var cat_selecturl:String =("http://onedev/one/Sophia/CourseQuery2.asp?Cat=" + cat_select);
                                var xmlq2:XML = new XML ();
                                var q2theURL_ur:URLRequest = new URLRequest("xmlq2.xml");
                                                       //replace with cat_selecturl ---- test with "xmlq2.xml"
                                var q2loader_ul:URLLoader = new URLLoader(q2theURL_ur);
                               q2loader_ul.addEventListener("complete", q2fileLoaded);
                                function q2fileLoaded(e:Event):void
                                                xmlq2 = XML(q2loader_ul.data);
                                                //trace (unescape (xmlq2));
                                               course_step1.prompt = "";

Answer 1

Check the HTML source. Is any code after the initial option present (ie the </select></td>)? If not then you are getting an error that is masked by the fact that you already committed the response. Look into your logs.
If the HTML source looks fine I fall back to my previous answer and you need to re-check the messages closer to where the work is being done. Though it never hurts to check the log files.