on form load i need to load my stringlist field by calling web service

hi
  
I have written my code for loading the stringlist datatype fieldname by calling the webservices.
  
code is as below
  
  
Sub Form_onload(Form)
  
' this is the function that i am calling the webservice
PopulateDropdown(Form)
  
end sub
  
  
Sub PopulateDropdown(Form)
  
1) i am call my webservice,  
2) this web service gives the xml response and this response, i am paring it and storing in one variable called "codes" and the sample datavalue in the variable "codes" is as below
  
codes = "a100;b200;c300;d400;f500;"
  
3) Now i am assigning or updatefiledset as below
  
Form.UpdateListField "productCodes", False, codes, ""
  
note :- here 'productCodes' is my stringlist field in my form i.e a dropdown box.
  
end sub
  
  
Issues
------------------------
  
As long as my service give the simillar response, i am not having an issue in dropdown list
  
but if my resonse gives a new values in that response, my form is not reloaded with new values in the stringlist filed on the form
  
i.e when i select my menu in the LED screen and in that menu, if i select my form then that form is not loaded with updated values.
  
  
hence is there any way for reloading the form in that menu itself.  
                                       or  
is there any way of reloading my menu, each and every time when i click on "OTHER Function" button in MFD.
  
Thanks
Chiranjeevi Yadav