Somebody has sent you a link to a page - but when you click on it in the mail message (or if you paste the link into your browser window), you get an "access denied" message.
Two possibilities exist:
A) You're not logged in to CROS .
B) If you're already logged in to CROS , you are not a member of the community to which the page is associated.
Solution (case A)
1) Log in to CROS
2) Click on the link in the mail message once more.
If access still is denied, although you're logged in, case (B) probably holds.
Solution (case B)
Contact the person responsible for the community (ESSnet project etc.) to which the project is associated, and ask to be added to the list of members of the community. Once you've been added, try Solution (A).