Mariadb/MyISAM: Incompatible key or row definition between the MariaDB .frm file and the information in the storage engine. You have to dump an
Try the following:

First check for all running queries and possible Connections your table might use. You can do this by 

SHOW PROCESSLIST;


which gives you all running queries/Connections. You can terminate a query/Connection by

KILL &lt;id&gt;;


After that repair your table

REPAIR TABLE myTable;


Try to run this more than once until your Status Returns as ok. After that 

OPTIMIZE TABLE myTable:


Then you can use the table again.