Two common mistakes when trying to log into eduroam are:
Using one's CLASSE credentials instead of one's Cornell credentials.
Omitting "@cornell.edu" from the username. You must log into eduroam as your-NetID@cornell.edu because eduroam is a cross-institution service.
If you have a CLASSE-managed laptop, you need to follow a special procedure to connect them to eduroam -- see ConfigureEduroam. By default, they'll try to use CLASSE authentication, which cannot work with eduroam.