change page in active sessions

Hi! I have a problem. Having 5 pages of active users I would like to change pages under “Active Sessions Management” (with arrows down on right side of the form of course). But when I click for the next page I have only a white page with this link: about:blank#blocked
I can only see the first page (even I change from 40 to 80 displayed sessions per page I have the same problem). Everything else works ok. Suggestions? Thanks!