I can export reports in IE just fine, but when I try to export in Chrome or Fire Fox I get an error. I have found that I only get the error with reports that use a SqlDataSource​ because when I created a test report that did not get external data it exported ok; but when I added the SqlDataSource and had it pull from SQL Server then it would no longer export. It always displays just fine though... it just won't export unless I (or my clients) use IE.
I've also posted this on Stack Overflow: http://stackoverflow.com/questions/31250011/telerik-reporting-cant-export-in-chrome-when-using-sqldatasource.
It has 14 votes so apparently someone else is having this problem... but no answers :(