it chrashes because ioSFV makes rather big .ioFTPD files..
ioSFV works best with 5.8.6+
Versions before that chrash on .ioFTPD files bigger than 4kb.
So again, search your hdds for .ioftpd files..
delete those over 4kb.. and voila your site will start without chrash.
and you can use them together.
Just use neoxed's remove-bad.ioftpd-files tool
nxiofilecheck
http://www.inicom.net/pages/en.ioftpd-scripts.php?did=9