MyBB SQL Error

MyBB has experienced an internal SQL error and cannot continue.

SQL Error:
1062 - Duplicate entry '0' for key 'uid'
Query:
REPLACE INTO mybb_sessions SET `uid`='0',`sid`='20b9729bf324ea53735f760a619e6e89',`time`='1495866396',`ip`='54.196.17.193',`location`='/forum/showthread.php?tid=33',`useragent`='CCBot/2.0 (http://commoncrawl.org/faq/)',`location1`='61',`location2`='33',`nopermission`='0'