Problem while running mpi program

Hi!

    I am running a parallel program and getting the attached err_log. The
problem seems to be strange as  some times the code runs normally with the
same input and some times not. If the cpu usage is low, mostly i am  not
getting this err_log..
 Actually, what the program does is:
when master gives a command to the slaves, they take data from the nfs
directory.  They create a temp directory in /tmp and after finishing the
work, the results will be copied back to nfs directory.
In this process some problem is coming. Actually this program worked fine
for a month or so,, But now suddenly, without changing the code and for the
same input we are getting this problem..
What could be the problem..??
Please help me in solving the problem..
Thanks in advance,
Kalyani