krenew command not working : Permission Denied

krenew command not working : Permission Denied

I am using a Linux server to perform my simulations. The login and the
file-system of the server are protected using kerberos. The file-system is
supported using NFS.
Since my simulations take a lot of time to run, my ssh sessions used to
hang regularly. So, I have started running my simulations in byobu
(similar to screen).
In order to make sure that my kerberos session remains active, I am using
the krenew command.
I have entered the following command in my .bash_profile file. (I am sure
that it is called for every login)
killall -9 krenew 2> /dev/null
krenew -b -t -K 10
So everytime I ssh to the server, I kill the existing krenew command.
Then, I spawn a new krenew command -b (which runs in background), -t (I
forgot why I was using this option !), and -K 10 (It must run after every
10 minutes and refresh the kerberos cache).
When I run the simulations, It runs for 14 hours and then suddenly, I am
getting error for reading file Permission Denied
Is the command that I am running incorrect ??