I have an link where i need to click and open report in the format needed.

pdf is working

http://localhost/ReportServer?%2fReport&rs:Command=Render&rs:format=pdf

xls is not working

http://localhost/ReportServer?%2fReport&rs:Command=Render&rs:format=xls

Reporting Services Error

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You have attempted to use a rendering extension that is either not
registered for this report server or it is not supported in this edition of
Reporting Services. (rsRenderingExtensionNotFound) Get Online Help

ShanmugaRaj