Critical error during update process

Support & Bugs
1

/home/activei1/public_html/piwik/core/Updates/0.4.3.php:
Error trying to execute the query 'DROP INDEX index_idaction ON piwik_log_action'.
The error was: SQLSTATE[42000]: Syntax error or access violation: 1091 Can’t DROP ‘index_idaction’;

Any advice ???

2

Reinstall 0.5.3 in a fresh folder.