An intermittent error I don't understand.

I'm new to ASP.net and using C# for the language. I wrote an application to track item moving from one location to another. Everything works fine in test and about half of the time in production but Occasionally I get an exception that I can't figure out. Any help would be great. When the user logs in I check for their access level I have stored in a Sybase database. The default page login code behind page has this code:
checkUserAccessLevel newUser = new checkUserAccessLevel();
               int currentUserAccessLevel = 0;
               currentUserAccessLevel = newUser.GetAccess();
The error message has the third line with the error plus a line in the class code file I am using.
Exception message: Object reference not set to an instance of an object.
 
Here is the ...