Working both with New and Old version of Ajax Tool Kit

I have an ASP.net web site built on framework 3.5 and it has used some calender extenders from older version of AjaxControlTool Kit. But now I want to have this BalloonPopupExtender in to the same site. So I downloaded new version of the Ajax toolkit (AjaxControlToolkit.Binary.NET35.zip) and managed to get the required tool. When I extend the textbox to put the BalloonPopupExtender it asked and replaced the AjaxControlToolkit.dll in the Bin folder with newer one.

Now my earlier used calenderextender does not work. If I replace the old dll again it works and not the BalloonPopupExtender .

How can I make both to work?