Remote XLS file problem

Hi guys!

We've got a problem with all excel files we're trying to edit with ZOHO sheet. Sample file is available at: http://files.wst-enelpa1.webnode.com/200000022-b357ab44bb/a.xls

We always receive this response:
RESULT=FALSE
ERROR_CODE=2502
WARNING=Internal Server Error while processing this request

Whats wrong?

Best reagrds

Lubos