WPF ComboBox Binding Errors -

i've searched hours , not find existing solutions problem i'm having. here please if can. when bind combobox selectedvaluepath seeing bindingexpression path errors in output window:

system.windows.data information: 41 : bindingexpression path error: 'geounitid' property not found 'object' because data item null. happen because data provider has not produced data yet. bindingexpression:path=geounitid; dataitem=null; target element 'combobox' (name=''); target property 'notarget' (type 'object')

system.windows.data information: 20 : bindingexpression cannot retrieve value due missing information. bindingexpression:path=geounitid; dataitem=null; target element 'combobox' (name=''); target property 'notarget' (type 'object')

system.windows.data information: 21 : bindingexpression cannot retrieve value null data item. happen when binding detached or when binding nullable type has no value. bindingexpression:path=geounitid; dataitem=null; target element 'combobox' (name=''); target property 'notarget' (type 'object')

system.windows.data information: 10 : cannot retrieve value using binding , no valid fallback value exists; using default instead. bindingexpression:path=geounitid; dataitem=null; target element 'combobox' (name=''); target property 'notarget' (type 'object')

the binding work correctly, , correct values displayed, suspect these errors reason poor performance seeing (scrolling/loading timing). here's relevant xaml:

   <listview x:name="lvitems" grid.row="1" grid.column="0"        itemssource="{binding elementname=mywindow, path=items, mode=twoway}"        gisc:listviewsort.issortable="true">         <listview.view>             <gridview>                 <gridview.columns>                  <!-- selecteditembinding: source:int32, dest:dest:int16  -->                     <gridviewcolumn>                         <gridviewcolumnheader tag="countryofissue" content="countryofissue" />                         <gridviewcolumn.celltemplate>                             <datatemplate>                                 <grid>                                     <combobox                                      itemssource="{binding elementname=mywindow, path=countries}"                                      selectedvaluepath="geounitid"                                                                                 selectedvalue="{binding path=countryofissueid, mode=twoway}"                                     displaymemberpath="shortname"                                      style="{staticresource grideditstyle}" />                                 </grid>                             </datatemplate>                         </gridviewcolumn.celltemplate>                     </gridviewcolumn>                 </gridview.columns>             </gridview>         </listview.view>     </listview> 

i've verified itemssource collection not have null items. i've tried entirely different structure (wpf datagrid instead of listview/gridview structure shown above similar results). scrolling performance terrible small number of rows (~400). searched ways improve scrolling performance, solutions did little help. there tons of these binding errors suspect root cause.

edit (added relevant types)

//listview collection (dependency property defined in usercontrol):

public static readonly dependencyproperty itemsproperty = dependencyproperty.register(     "items",     typeof(corpactionautopostconfigs),     typeof(corpactionautopostconfigcontrol2) );  public corpactionautopostconfigs items {     { return (corpactionautopostconfigs)getvalue(itemsproperty); }     set { setvalue(itemsproperty, value); } } 

//the type (observable collection) listview bound to

public class corpactionautopostconfigs : observablecollection<cadb.corpactionautopostconfig>, icloneable {     //code omitted } 

//the collection item type (defined in assembly don't have source code). wrote relevant public property below.

cadb.corpactionautopostconfig {     public int countryofissueid {set; get;} } 

//combobox items collection (dependency property defined in usercontrol)

public static readonly dependencyproperty countriesproperty = dependencyproperty.register( "countries", typeof(countries), typeof(corpactionautopostconfigcontrol2) );  public countries countries {     { return (countries)getvalue(countriesproperty); }     set { setvalue(countriesproperty, value); } } 

//the type (observable collection) combobox bound to

public class countries : observablecollection<rds.country> {     //code omitted } 

//the collection item type (defined in assembly don't have source code). wrote relevant public properties below.

rds.country {     public int geounitid {get;}     public string shortname {get;}   }