User Access in a custom page in WSS

Question

I have an ASP.NET app that runs under WSS. Will the credential of the user be passed? The users (readers by default) of my app can't access it but administrators can. It's like this. I have a page that displays some properties of a custom list item and enumerates its attachment files. Users can't access the page if a list item has at least one attachment. Anything in mind why this is happening? Could it be some sharing violation that is not necessarily SharePoint related? :)