I think I had the same issue--- if I remember correctly I edited the fsl_sub and overrode the queue to long.q or all.q (whatever the default queue name is on your cluster).
I think there's some bug (which I thought was on my end) of FSL trying to infer the default queue name for my SGE set up--- there's somethiing wrong with this command so it's not returning the default queue name for your setup-- so instead has a NULL value-- and then when the qsub runs it thinks the -m option is your queue name; hence the error.... it's running smething like qsub -q -m; i.e. not setting a queue.
I didn't have the time to really figure out why it was being goofy so I just uncommented out the #queue part and I believe that fixed the problem. I didn't have to to do this on one of my machines so I am not sure if it's because the version of SGE is different between the two machines, or more likely I just slightly screwed up the installation on one of them.
/usr/share/fsl/5.0/bin/fsl_sub
# SGE should already have a default queue
#queue=long.q
mailto=`whoami`@${fslcluster_mailto_domain}
MailOpts=${fslcluster_mailopts}
--- This is how I just set it up-- manually specified the default queue name
# SGE should already have a default queue
queue=all.q
mailto=`whoami`@${fslcluster_mailto_domain}
MailOpts=${fslcluster_mailopts}