monkeyscan: python subprocess OSError: [Errno 2] No such file or directory

I'm getting this when trying to sign a key:

found 1 keys matching your request Traceback (most recent call last): File "build/bdist.linux-x86_64/egg/monkeysign/gtkui.py", line 539, in decoded File "build/bdist.linux-x86_64/egg/monkeysign/gtkui.py", line 562, in process_scan File "build/bdist.linux-x86_64/egg/monkeysign/ui.py", line 359, in export_key File "build/bdist.linux-x86_64/egg/monkeysign/ui.py", line 405, in sendmail File "/usr/lib/python2.7/subprocess.py", line 710, in __init__ errread, errwrite) File "/usr/lib/python2.7/subprocess.py", line 1335, in _execute_child raise child_exception OSError: [Errno 2] No such file or directory

* I could provide a full debug log, if this would be helpful and needed. However, as there are some key IDs etc. inside which I don't want to share, to begin with just the above extract. * I tried to debug this shortly: I'm unsure which file or directory this is about. The tmp keydir inside `/tmp/` gets created and populated correctly. * If there is anything I can do to debug this further or you need additional information, please let me know. * `$ monkeyscan --version 2.x` * `$ git log --oneline | head -n1 8a0bae14 Merge branch 'sidebar_logo' into '2.x'` * `$ gpg --version | head -n1 gpg (GnuPG) 1.4.18` * `$ gpg2 --version | head -n1 gpg (GnuPG) 2.1.11` * `$ dpkg -l | grep "python-qrencode\|python-gtk2\|python-zbar\|python-zbarpygtk" | cut -d " " -f -40 ii python-gtk2 2.24.0-5 ii python-qrencode 1.2-1 ii python-zbar 0.10+doc-10+b1 ii python-zbarpygtk 0.10+doc-10+b1` * Debian environment with software out of jessie, jessie-backports and stretch