After Oracle SSO enabled edelivery.oracle.com, we were unable to access the site through Opera browser. Whenever we clicked on Sign On/Register button a screen with Oracle Access Manager would come up with
System error. Please re-try your action. If you continue to get this error, please contact the Administrator.
A google search revealed the answer from OTN. You have to make Opera identify itself as Internet Explorer. It works fine then. This is from http://www.opera.com/support/kb/view/843/
Go to edelivery.oracle.com. Click on Sign in / Register button. Wait for the error to appear.
Right click anywhere on the site, click Edit Site Preferences.
Click the "Network" tab
In the "Browser identification" drop-down, select "Identify as Internet Explorer" or "Identify as Firefox"
Reload the page