IE6/7 hangs: GetCommand('').Execute

hello,

Internet Expolorer 6 and 7 crashes with the following:

function FCKeditor_OnComplete( editorInstance )
{
editorInstance.Commands.GetCommand('JustifyLeft').Execute();
editorInstance.Commands.GetCommand('JustifyCenter').Execute();
}

I have 2 editors on one page and at the second time the editor called OnComplete -> IE hang up.
Actually I only want to Change the default alignment from left to center (see: viewtopic.php?f=5&t=4989&p=22147)

I also try it in a seperate funktion with the same result:

var oEditor = FCKeditorAPI.GetInstance('edit1') ;
oEditor.Commands.GetCommand( 'JustifyLeft' ).Execute() ;
oEditor.Commands.GetCommand( 'JustifyCenter' ).Execute() ;

var oEditor = FCKeditorAPI.GetInstance('edit2') ;
oEditor.Commands.GetCommand( 'JustifyLeft' ).Execute() ;
oEditor.Commands.GetCommand( 'JustifyCenter' ).Execute() ;

does anybody know how to solve this problem or how to change the default alignment?