' Ext.eventobject ' is empty or not an object's error cause and workaround

Environment:
IE7.0, Ext JS 2.2

Error behavior:
IE Browser error:
Line: 1670
Char:4
Error: ' Ext.eventobject ' is empty or not an object
Code: 0
Url:......
Firefox browser is OK.

Error Reason:
Many times in the Web page to introduce Ext JS Lib.
I am a page set up some frame,frame all the pages are referenced Ext JS JS package.

Workaround:
Delete Extra references (I did)
You can also test whether it has been introduced before introduction (for example, to detect the presence of Ext objects, without testing)

Extended:
Ext JS JS package can not be introduced many times, or it will produce a series of anomalies, such as the panel collapse time also retains the following space and so on.