Access issue after installation!

Hi

I have installed wordpress on my webserver. I did the 5 min setup and everything went ok. I received an email stating:
Your new WordPress blog has been successfully set up at:

http://www.niallkeogh.com/blog/wp-admin

When I click the above link, I get a “You are not authorized to view this page” blank page error.

Any ideas??
Thankyou in advance.