ERROR in place of usernames in Global Security

[LC]

Hi,

I have a set of users on Jenkins and currently all but two of the usernames
are replaced with ERROR in the Configure Global Security page. When I click
on ERROR, I get this message:

Forbidden

You don't have permission to access
/jenkins/descriptorByName/

hudson.security.GlobalMatrixAuthorizationStrategy/checkName
on this server.

Has anyone had this issue before and/or know how it can be solved?

Thanks,

LC