My Y axis is not long. 400 mm tops
This is not necessarily what your problem is, because those helpful error messages often point in the wrong direction. But ...
Servos have to have a following error to work. When the axis is where it is supposed to be, then they don't move. When you give it a command, say, "go ten inches plus at a feedrate of 250 ipm" then there is immediately an error between where it is and where you told it to be. That's called following error and the control and drive adjust the current to the motor depending on how big that error is to speed it up or slow it down.
The computer has a range of following error it allows. If the amount allowed was zero then it would error out all the time because nothing can move instantaneously. But if the error gets too big, then the axis can get ten feet behind where it's supposed to be, which is detrimental to accuracy.
So the drives are adjustable. Analog ones are, anyhow, I don't imagine these are digital ? If they are, ignore everything I just said
What appears possible is that your electronics have drifted out of range, so the motor is not being goosed enough to keep the following error within tolerance, which generates an error message and shuts down the control. This usually won't show up in a real short move, like 1" or so, but 16 inches at rapid ought to be plenty of motion to get too far behind.
First thing I would do is get out the electronics manual and look for the procedure to tune up the drives. Do all of them so they are the same, then your circles will be rounder and your angles will be straighter. Being absolutely on the money is not as important as getting them all the same, especially X and Y.
You should do this anyhow because electronics do drift over time. The whole machine will run noticeably better if you do.
If you haven't done it before, it's useful to have someone who knows what they are doing do the adjusting while you watch and ask questions. Is ewsley near you ? It's worth the investment ...
Again, if your drives are digital then I'm all wet, ignore me
This is what digital is supposed to avoid.