Ext.LoadMask crashes:

Code:
    <SCRIPT TYPE='text/javascript'>
        Ext.onReady( function() {
           var mask  = new Ext.LoadMask(Ext.getBody(),{msg:'hola'});
        });


    </SCRIPT>


with the following error:

Code:
Uncaught TypeError: Cannot read property 'isDetachedBody' of undefined
Ext.define.flushInvalidates                     ext-all-debug-w-comments.js:75182
Ext.define.run                                  ext-all-debug-w-comments.js:75633
Ext.define.statics.flushLayouts                 ext-all-debug-w-comments.js:60170
Ext.define.statics.updateLayout                 ext-all-debug-w-comments.js:60208
Ext.define.updateLayout                         ext-all-debug-w-comments.js:62550
Ext.define.setSize                              ext-all-debug-w-comments.js:62491
Ext.define.initComponent                        ext-all-debug-w-comments.js:61122
callParent                                      ext-all-debug-w-comments.js:4933
Ext.define.initComponent                        ext-all-debug-w-comments.js:77027
Ext.define.constructor                          ext-all-debug-w-comments.js:61080
callParent                                      ext-all-debug-w-comments.js:4933
Ext.define.constructor                          ext-all-debug-w-comments.js:76986
constructor                                     ext-all-debug-w-comments.js:5946
Ext.define.constructor                          ext-all-debug-w-comments.js:81460
constructor                                     ext-all-debug-w-comments.js:5946
(anonymous function)                            index_test.html:18
isEvent                                         ext-all-debug-w-comments.js:12414
fire                                            ext-all-debug-w-comments.js:12556
Ext.EventManager.fireDocReady                   ext-all-debug-w-comments.js:12691