We have an Arrow1000 with A2100 control and kollmorgan drives/ motors; at startup we have a z axis grid failure when trying to home the machine. All axes move after powered up; all register movement on the display screen. When homing, we get the z- axis grid failure. We checked the TPA and Limit switch on z through programware and visually, all ok. Checked continuity on wiring from the drive to the A2100 board, all ok. Slowed the feedrate down as suggested on other posts, no help. Any ideas?