Server error during the "image-stitch" request

The server raises the following error:

Traceback (most recent call last): File "/home/ubuntu/cloudcv/cloudcv17/app/celery/web_tasks/ImageStitchingTask.py", line 25, in runImageStitching popen = subprocess.Popen(list,stdout=subprocess.PIPE, stderr=subprocess.PIPE) File "/usr/lib/python2.7/subprocess.py", line 710, in **init** errread, errwrite) File "/usr/lib/python2.7/subprocess.py", line 1327, in _execute_child raise child_exception OSError: [Errno 2] No such file or directory