@roger64: The jpegtran version that you've installed is the fork that I mentioned that still uses the old syntax and will most likely not work.
I'd recommend the following workaround:
1. Install the Wine windows emulator, if you haven't already done so.
2. Change lines 83 and 85 in plugin.py as follows:
old version:
Code:
exe_path = 'jpegtran'
args = [exe_path]
new version:
Code:
exe_path = os.path.join(SCRIPT_DIR,'win', 'jpegtran.exe')
args = ['wine', exe_path]
Make sure not to mess with the indentation otherwise Python will display some cryptic error messages.