[web2py] too many redirect message when using login

[man24]

I am new to web2py and has been following the online book to learn it.  I 
was following the 'wiki' example and everything worked fine the first time, 
however, today when I click on any action that requires login or even the 
login link in the menu, web browser cannot open the page and gives 
following message:  'too many redirects occurred trying to open the page'. 
 I am using web2py on a mac.  Thanks for your help.