Getting RunTime Error in webforum created in Asp.net with C#

I am facing a strange issue. Recently i have two pages http://www.systotech.com/pdf-split.aspx and http://www.systotech.com/pdf-merge.aspx both are working well. Then i need to create a single page for both of them, and I merged the code. The code runs fine in my local browser but when i have uploaded the code on server results in Run Time Error

Runtime Error

Description: An exception occurred while processing your request. Additionally, another exception occurred while executing the custom error page for the first exception. The request has been terminated.

http://www.systotech.com/pdf-split-and-merge.aspx

I've turned custom error mode off, but can't figure out where this error is coming from.