EXTJS tree panel drag and drop Exception

I have two tree panels tree1 and tree2 and one form panel in my application.I added drag and drop plugin for both the tree panels.If i drag from any leaf node from tree1 panel to form panel,the particular details of that node will display in form panel and the selected leaf node get updated in the tree2 panel. Now if i drag and drop any leaf node from tree2 panel,the particular details of that node in form panel and selected node from tree2 panel has to be removed. I can accomplish what i said so far.

Now once again,if i try to add drag and drop operation for tree1 panel after remove operations performed in the tree2 panel i am getting the following exception........

uncaught exception: [Exception... "Component returned failure code: 0x80004003 (NS_ERROR_INVALID_POINTER) [nsIDOMHTMLDivElement.insertBefore]" nsresult: "0x80004003 (NS_ERROR_INVALID_POINTER)" location: "JS frame :: http://extjs.cachefly.net/ext-4.0.2a/ext-all-debug.js :: :: line 15686" data: no]

Any help appreciated... Thanks in advance.....