I have figured out that this problem is between El Capitan and Super Duper, a backup program from Shirt Pocket. Updating my OS from 10.10.5 to 10.11 caused Super Duper a problem. An update to Super Duper was posted and I installed it (v 2.8 v96), but the Super Duper scheduled backup that was to run this morning still posted the error:
sh:/usr/bin/lockfile no such file or directory.
I opened Super Duper's scheduler to try to start the desired backup from the scheduler interface. The error message appeared again. I then started a backup using the control panel rather than the scheduler. The backup ran. I then redid the scheduler. That seems to have eliminated the error message.