This could be because Sencha is trying to be too clever and tries to cater for browser specific behaviour, try setting the following to 0 in your config.xml (they are all 1 by default):
In the config.xml file that comes with RhoElements, these values (with the original values set to "1") appear under an XML NPAPI as follows::
Should I modify these or place the settings in the existing <Preloads> that reads:
One more item of note... the project is structured with several JS files referenced by the HTML file. I have put code in each of these to cause an alert() to be raised and it gets through parsing them all so that suggests these files don't have any problems in the JS that would break the loading. One thing I did notice is that all of the alerts fire BEFORE the RhoElements registration screen comes up. Once the final event (the Sencha OnReady event) fires and raises an alert, the registration screen comes up.
Also, Sencha appears to be initialized. If I call Ext.Application multiple times, I get the error from Sencha that the application has already been created.