The program is unable to create a reduction file as specified. The most probable cause is due to the directory where the file creation is to be performed being protected against write access, or does not exist at all. Type:
% ls -l /name/of/directory
to verify that the file exists, and to see what access rights the current directory has.
If you own the directory in which file creation was attempted and have the required access rights then the most probable cause is the exhaustion of system resources required, most notably disk space. Type:
to see if you have run out of space.