For Windows Phone 7 the highest possible to download version of Tasks is v.1.37 into which only Exchange sync is supported. You have tried to add the Telerik cloud provider credentials for the Exchange provider, that's why you've got such an error.
The Telerik cloud sync option is supported only into Windows Phone 8 versions of Tasks (WP1301 is the latest available for download at the Marketplace).
TRY TELERIK'S NEWEST PRODUCT - EQATEC APPLICATION ANALYTICS for WINDOWS PHONE 7.
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