When using a Restful Store the remove command is throwing an error (Line 1717 of ext-base-debug Error: Invalid argument) when it tries make the DELETE ajax request. Specifically the error is occurring in the asyncRequest method in ext-base when o.conn.send(postData || null); is called. I created a standard Ajax request and used the DELETE method along with the same URL and it worked fine. All other actions in the Store (Create, Read, and Update) work fine.
The EXT JS example RESTful store throws an error as well located here: http://www.sencha.com/deploy/dev/examples/restful/restful.html
I tracked down the problem which stemmed from using the ext-basex user extension. If you are using ext-basex try overriding the forceActiveX boolean by adding this to your overrides: Ext.lib.Ajax.forceActiveX = true;