The E-PID fault is caused by a significant difference between a control software set position and an actual position of a motion controller. 
It is generated by low-level motion controller safety algorithms when:
1. Control software failure.
In this situation, it is recommended to reinstall the control software.
The situation is very rare, but you should take it into account, especially in the case of Mach3 CNC software.
2. The configuration file of the control software has been corrupted.
In this situation, it is recommended to reinstall the control software and configure it manually. The situation is very rare, but you should take it into account, especially in the case of Mach3 software.
3. Control software mistake in generating trajectory.
4. Unknown plugins or language-changing packages installed in the control software.
The situation concerns Mach3.
5. In the case of CSMIO/IP-A controllers there are problems with:
a) feedback,
b) a servo drive (servo driver + servo motor),
c) tuning of position PID regulator of the controller,
d) tuning of velocity PID regulator of a servo drive.
6. Strong network transmission interference, leading to controller’s data buffer exhaustion, which may cause jerks in machine work.
More about this is described in this article: What causes network connection issues [simCNC, Mach4]?
7. A computer network card or computer has energy-saving modes that affect the stability of the network connection.
More about this is described in this article: What causes network connection issues [simCNC, Mach4]?
8. A low-quality power supply, which cannot work in industrial conditions, was used to power the motion controller.
9. No motion controller support for some (mostly little used) functions of the control software.
It happens in the case of Mach3 and Mach4, due to specific solutions used in this software, the functions will never or not in the nearest future be supported by CSMIO motion controllers.
Mach3 – It is not recommended to use the G31 command in Mach3 versions newer than 03.043.044.
The older versions allow G31 to be used only from the macro level.
Mach4 – This software is continuously developed as well as the CS-LAB plugin, therefore the situation may change dynamically.
SimCNC – This control software does not encounter this problem as the control software and firmware of the CSMIO motion controller controllers are created by the same developers.
10. The CSMIO/IP-S or CSMIO/IP-A motion controller was damaged.
The situation is theoretically possible and should be considered last.
