c# - DropDownList DataSource set to EF bindingsource gives "The property 'BackupFileID' is part of the object's key information and cannot be modified." -

i have combo box(dropdownlist) data source bound backupfilesbindingsource, displays backup file paths members of list. when selection in dropdown changes, loads image picturebox on form.

in form_load have following:

            backupfilesbindingsource.datasource = this._entities.recordbackupfilepaths                                                             .where(x => x.recordid == _selectedrecord.recordid);             if (_uiimagesqcombobox.selectedindex == backupfilesbindingsource.count - 1)             {                 // ensure image displayed                 _uiimagesqcombobox_selectedindexchanged(this, eventargs.empty);             }             _uiimagesqcombobox.selectedindex = (backupfilesbindingsource.count - 1); 

when have more 1 backup file, when form loads, error:

"the property 'backupfileid' part of object's key information , cannot modified."

which thrown @ reportpropertychanging("backupfileid");

    [edmscalarpropertyattribute(entitykeyproperty=true, isnullable=false)]     [datamemberattribute()]     public global::system.int32 backupfileid     {                 {             return _backupfileid;         }         set         {             if (_backupfileid != value)             {                 onbackupfileidchanging(value);                 reportpropertychanging("backupfileid");                 _backupfileid = structuralobject.setvalidvalue(value);                 reportpropertychanged("backupfileid");                 onbackupfileidchanged();             }         }     } 

dropdownlist binding settings:

i understand backupfileid property key, can't understand attempted modified, since doing changing selected item in dropdownlist.

thanks help!