Get me? (12/12/2014)

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Not experienced this issue but as a workaround you can enable Excel xls rendering in SSRS 2012.

You need to edit the rsreportserver.config file. Find the extension for EXCEL and remove the Visible="false" attribute. If memory serves correctly you also have to rename it, I changed EXCEL to "EXCEL 97", otherwise it doesn't show in the dropdown. Once the config has reloaded you should see two options in the export dropdown, Excel for xls and Excel 2003 for xlsx.

Marcel Prooust

Thanks for the respond and solution, however, we don't want to open the file in xls format but keep xlsx format. Is it any to do with Excel side security? any Active x plug in needed? and SP for the hot fix?