Problem in outlook 2003 connectivity using Exchange Server

I am getting  problem with exchange 2010 connectivity in outlook 2003 using RPC/http protocol. 
But if I use auto discovery connection in outlook 2007 then there is no issue at all.

How to fix this problem ?

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I am getting  problem with exchange 2010 connectivity in outlook 2003 using RPC/http protocol. 
But if I use auto discovery connection in outlook 2007 then there is no issue at all.

How to fix this problem ?

If you get the following error message after migrating over to Exchange 2010:
Cannot start Microsoft Office Outlook. Unable to open the Outlook window. The set of folders could not be opened.

It is because the default with Exchange 2010 is encrypted RPC traffic.  This is easily rectified, you can find the encrption setting in MS Exchange mail properties under control panel for the PC.  See here for more information.

Here is the wonderful guide to configure Exchange account in the outlook
http://www.msexchange.org/tutorials/outlookrpchttp.html