Could you please use error_reporting(E_ALL); on top of page so that php will give you detail error rather than just general 500 error code.

How many rows were you trying to export? If it's a lot pls consider using BigSpreadsheetExportable, which uses stream to read/write to save memory and time at the cost of less customization and chart, instead of ExcelExportable, which normally requires more memory and time but is more customized. Here's the demo:

http://localhost/htdocs/KoolReport/koolreport_examples_dong/reports/excel/big_spreadsheet/

The example code is at the end of the page. One note is that to export to CSV with big spreadsheet you still need an excel view instead of using a datastore name directly.