ASP.NET by default won't allow input files greater than 5MB.  You will need to edit the httpruntime element (http://msdn.microsoft.com/en-us/library/e1f13641.aspx) and increase the maxRequestLength & exectionTimeout properties in the web.config file to increase this limit.

The web.config file is located in your project root, and you can open it with notepad. 

In the web.config:

1. MOST IMPORTANT STEP - Backup the existing web.config file.  If you run into problems you'll be able to restore this backup.
2. Find <system.web> in the web.config file.  Add a line break to create a new line underneath <sytem.web>.
3. On the new line you just inserted, input this: <httpRuntime maxRequestLength="10000" executionTimeout="300" /> 
4. Save the file.  Test and see if it works.
5. IF YOU RUN INTO ANY PROBLEMS RESTORE THE BACKUP YOU MADE IN STEP 1

This should allow you to input files up to 10MB in size without problem.

CAUTION:  The method in this article will increase the file size limitation and may cause extreme database growth to be experienced.