It looks like you are using a command task to execute the script. Try running the script from the Unix/Windows command editor and see what error you are getting there. It could be a permission issue on the directory you are copying the file into.
from the unix command line it works.when i touch a file here /apps/informatica/95/server/bin here it works.
Are the Unix and Informatica users the same?
As correctly pointed out by Srikanth, it may be due to the permission of the user running the command task in which unix script is getting called..
Also if you can tell what is ur unix scritp doing or if you can share your script then may be we can help you better..
You can also look at the following KB related to the exit code 256
Try enabling a log file for the script and enable verbose mode execution inside. That shall log the error msg in the script log file when executed, which we can then use to debug the issue.
You can enable it by adding the below 2 lines at the begining of the script -
exec 1>log-file-name-with-path 2>&1
Once you execute the script, check the log-file-name created and that shall have all the error & output msgs from your script inside logged - which you can use to find out the issue.
If you have any resrtictions in changing the shell-script code - then atleast change the script invocation in the command task to execute as below -
ksh -vx shell-script arg1 arg2 1>log-file-name-with-path 2>&1
Let us know how it goes.
One other thing I would like to enquire is - are there any wild-card characters like  or * or ? which you are using in your files names of the cp command? There are scenarios where these might bomb
I restarted informatica and it is working now
So again the restart did the trick..
Glad that your issue got resolved, but the exact cause is stil unknown..
Do try things suggested by experts and also in the KB articles if you face similar issue in future..