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:
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.