Since the RadXmlHttpPanel provides the ability to pass a string, it is up to you how to organize this string. What I suggest is to concatenate all the parameters separated with some separator sign and form one resultant string which contains all the parameters and pass it as a value. After that you should simply split the string according to the used separator on the server and you will get your multiple parameters. This is a standard ASP.NET technique which is not directly related to RadControls and I believe that it will be helpful in this case.
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