I had this same issue.
I read a suggestion somewhere to write a shell script which just contains the command to run the python script. So something like:
#!/bin/sh
/usr/bin/python /opt/openhab/configurations/scripts/lifxstate.py
Save that lifxstate.sh.
Then chmod +x lifxstate.sh to make it executable.
Now try
executeCommandLine("/opt/openhab/configurations/scripts/lifxstate.sh")
No idea why this works, but it does for me.