what does this mean?

What does this really mean:  'Recording failed because the program could not be found in the guide'?  I always thought it meant the program got rescheduled or moved or preempted pr something.  'Lucifer' on fox did not record last night with this error but it was on at it's usual time as it is available in the on demand (which is where I will go to watch it).  

I get several of these messages a month and am now concerned we are missing shows completely thinking that they got rescheduled.  

So what does this really mean and why does it happen?