Usually occurs in a group, I found today that I had a group of 5 computers in the current tasks folder and I ran the deployment on those. All of them failed, but the option to continue on failure is checked. I was able to successfully single install on 4 of the 5, but the last one failed again and again.
The next 'group I did also failed on all clients and this group did not contain the failed one mentioned above.
So typically on groups, but not limited to.