MySQL: #126 - Incorrect key file for table

Question

I got the following error from a MySQL query.

#126 - Incorrect key file for table

I have not even declared a key for this table, but I do have i

Answer 1

Every Time this has happened, it's been a full disk in my experience.

EDIT

It is also worth noting that this can be caused by a full ramdisk when doing things like altering a large table if you have a ramdisk configured. You can temporarily comment out the ramdisk line to allow such operations if you can't increase the size of it.