Hello Yuki,

Could you give me hints about where to find these files. I have a look in the installation folder of Cassandra and in the /var/lib/cassandra folder?

Thanks very much for your help.
That was bug in 1.1.1 and fixed in https://issues.apache.org/jira/browse/CASSANDRA-4331.
Workaround is deleting the key cache files for your index CFs should fix this.