Hi,
on 2014-08-02 somewhere shortly around 0:00, some wikimetrics instances ran out of available database connections to labsdb, and hence failed to properly validate cohorts, and run reports. Since 9:00, wikimetrics again has enough database connections, and cohort validation and running reports should work again as expected.
We're tracking the issue at https://bugzilla.wikimedia.org/show_bug.cgi?id=69043
For metrics.wmflabs.org, I checked for affected cohorts and reports, but could not find any.
But in case you ran into issues during on metrics.wmflabs.org between 2014-08-02 00:00 and 09:00 it might be related to this issue.
Best regards, Christian