Why do you use $DBI::errstr? Oh, i see, the docs for DBD::mysql mix it up. Try looking at $dbh->errstr (as seen in the examples at the top of the documentation) instead to see if there's a difference.

Did you

1. try the statement directly in the mysql client?
2. make sure no other transactions are currently locking the table?
3. try $dbh->ping() as a basic test to see if your connection to the database actually works?
4. check what $dbh->errstr shows directly after the DBI->connect() call?
5. re-install/recompile DBD::mysql to make sure you are using the correct version of the C library?
6. check the database logfiles? Is there anything in them that might hint at an error?