@phip1611 are you able to reproduce this issue or it happened only once? It looks like a temporary issue while creating records in piwik_sequence table (race condition). IMO it should not happen again unless you try to select reports for other date ranges (e.g. August 2014), there are no archives for this month and there’s a MySQL hiccup.
That has happened to me on several occasions, the most recent being Monday, 1 Feb. My site has very low visit counts – on the order of 30 or so per day. I’m still using Piwik version 2.14.3
Always, the error goes away when the dashboard is reefreshed.