DBD::mysql::st execute failed: called with 2 bind variables when 6 are needed [for Statement "..." with ParamValues: ...] at ./pt-table-checksum line 7216.
The fix is simple: upgrade (or even downgrade) DBD::mysql to any version except 4.014. To see which version of DBD::mysql a system has, execute:
perl -MDBD::mysql -e 'print $DBD::mysql::VERSION, "\n";'
This bug may affect other Percona Toolkit tools, but currently pt-table-checksum 2.0 is the only victim. This bug does not affect pt-table-checksum 1.0, and it cannot be worked around in pt-table-checksum 2.0 because the bug in in DBD::mysql.
This bug affects pt-table-checksum 2.0 but not 1.0 because the newer version uses prepared statements with parameter values, whereas the older version does not. It seems, although I have not verified this, that DBD::mysql 4.014 has some sort of caching mechanism which causes it to use the wrong prepared statement.