First of all change in file system is an event. Checking it in cycle is bad idea. The better way is using event and process it as soon as it fires. So, you should redesign your solution.
Most likely
FileSystemWatcher Class (
FileSystemWatcher Class (System.IO)[
^] ) can help you.
And also. You should manage access rights properly, especially if you create ASP application. Improperly set access to folders could lead to denial of access or to security flaw (hacker can access your monitored folder).