Update doesn't finish

I was trying to update my piwik and unfortunately I get a Fatal Error, here the code:

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’; check that column/key exists

I hope you can help me.

Thank you in advance.