WEbListbox problema javascript childen of null

Could not execute returned javascript: Cannot read property ‘children’ of null
Source: RS.controls[‘BK5RtIhK’].insertRow(36,["enmanuel "]);
RS.controls[‘BK5RtIhK’].setCellContents(36,1,“0”);
RS.controls[‘BK5RtIhK’].setCellContents(36,2,“N/A”);
RS.controls[‘BK5RtIhK’].setColumnHeading(0,‘Usuarios ( 36 )’);

me da este Error alguien podria DEcirme el porque?

y este error tambien

Unhandled OutOfBoundsException
Message:

Stack: