If an ASP.NET page is redirecting in a never ending loop the most common cause is the use of an aspx page as a Custom Error.
Take the portion of the web.config file below as an example:
<customErrors mode="RemoteOnly" defaultRedirect="/error.aspx">
If the error.aspx page itself has an error it will redirect to itself over and over.
The recommended approach is to use static (.htm) error pages where practical. Alternatively disable custom errors temporarily while debugging the problem.