In answer to your question phpmyadmin is free to use but it depends on what your host has loaded, whichever database management/manipulation software you have it should have an option to repair or optimise your table(s), this is what KH99 is talking about, either by using built in software or using ssh to repair the guest table, if you do this you can turn that mod back on and all wil be well
It's not the fault of the mod, turning it off alieviated the problem because it calls on the guest table.