Update: It appears that the issue is resolved, and that the system is back up. iTunes Connect is down as Apple sorts out issue that caused some developers to be logged into wrong accounts.
Joe Rossignol, MacRumors:
A number of iTunes Connect developers have turned to Twitter and tipped us off about an ongoing issue where users are being shown someone else's session after attempting to login into their own account. Instead of seeing their own apps, iTunes Connect is mismatching users and displaying other apps from completely different developers. MacRumors has been able to duplicate this issue, which appears to be widespread and has been going on since at least 8 AM Pacific.