The first thing to check is to ensure that you have the latest Service Packs installed. At time of writing for VP2014, this was SP2 and Subscription Release 1 Service Pack 1.
Next check that the account that Vault uses to log into the Job Processor, has the necessary level of permssion on the file it is being asked to process. You can easily check this, by logging into the Vault client application as that user.
Another check, is to try manually to process the file. So if the SyncProperties and Update View is triggered because the file has been pushed from Work In Progress to Released, then, whilst the file is in the released state, (and you are still logged in as that same JP user), try Synchronising the properties locally and sending them to the Queue. Repeat for the Update View.
I recently had the odd behaviour where the above troubleshooting steps worked fine for 1 or two files. But sooner or later, the files failed with the message...."File Locked". There were multiple AVFS's each with one JP client except for one which had two JP clients. All worked perfectly except for the AVFS with the two JP clients.
JP#1 would start happily processing the files. Until JP#2 woke up and begain taking jobs from the queue. Then all jobs in the queue were rapidly processed but failed.
The (temporary) solution here is to only have 1x JP per AVFS.
At this time, I am not sure if AVFS was a factor or if it is reproducible in earlier versions of Vault. I reproduced the behavior with AVFS in VP2014 and development are looking into resolving it. I am sharing this experience in the hope that you dont spend as much time investigating this as I did.