Excel File Alternatives

[Jim Heavey]

I need to create a simple excel file via a console application (C#) which is
schedule to run on a perodic basis.
I first attempted to create and XML file, but when I opened this file up in
excel, it took about 25 minutes to load (about 40,000 rows to the excel file
with about 15 columns). Given the amount of time it took to bring up the
file, I did not consider this to be a viable alternative.
I then created a native Excel file from within the application, and this
works just fine when I run the application interactively. When I schedule
the job to run, I run up against a security error. Upon research Microsoft
does not recommed nor support this method.
I could create a comma delimited file, but then the user has to go through
the hassle of parsing the file each month and each time they access the file
(as they have no ability to save their changes.
So what method would be appropriate for being able to launch a scheduled C#
application and creating an excel file?

Thnaks in advance for your assistance!