MySQL table is marked as crashed and last (automatic?) repair failed

If your MySQL process is running, stop it. On Debian:

sudo service mysql stop

Go to your data folder. On Debian:

cd /var/lib/mysql/$DATABASE_NAME

Try running:

myisamchk -r $TABLE_NAME

If that doesn't work, you can try:

myisamchk -r -v -f $TABLE_NAME

You can start your MySQL server again. On Debian:

sudo service mysql start

Try running the following query:

repair table <table_name>;

I had the same issue and it solved me the problem.