Just a bit of additional information. This started about a month ago, and occasionally power cycling would get it to go away. Now it is always throwing an error. I've found references to "- overflow" in the manual, but don't fully understand what they are saying.
Rotary axis with limits and multi-turn rotary table
The relative actual position obtained using the equation on page 23 is displayed as it is. With the
multi-turn rotary table, whether or not relative actual position data is expressed within 0° and 360°
when the NC is reset can be set at NC optional parameter No. 2, bit 1.
When the additional axis is removed with the removable axis specification, “-OVERFLOW” will be
displayed as relative actual position data.I cannot rotate the axis, even in manual mode.When the relative actual position value is smaller than -99999.999 mm (-9999.9999 inch for
the inch system), “- OVERFLOW’ will be displayed on the display screen.