sql server - LongListSelector in Windows Phone 8 -

i encountring issues longlisselector in windows phone 8.

i display list, problem being entity of sql database retrieved wcf dataservices. wrote function return elements of problem observablecollection:

private observablecollection<problem> createproblemgroups() {      observablecollection<problem> listpb = new observablecollection<problem>();      var l = (from lp in problems lp.idproblem == lp.idmainproblem select lp).firstordefault();      listpb.add(l);      return listpb; } 

then, in load event of long list selector (called listproblems), bind previous observablecollection item source of listproblems:

private void listproblems_loaded(object sender, loadcompletedeventargs e) {      observablecollection<problem> data = new observablecollection<problem>();      data = createproblemgroups();      longlistproblems.itemssource = data; } 

the code compiled no error , application runs fine, nothing displayed in end.

i tried test tutorial msdn (http://msdn.microsoft.com/en-us/library/windowsphone/develop/jj244365(v=vs.105).aspx) getting xaml parse exception, stating: "cannot find resource name/key addrbookjumpliststyle [line: 52 position: 17]"

thank in advance help.