RF interference can affect the Wiegand signal returning a System Kit on the reader cable. To address this issue, use a Toroid Choke Core around the wire going back to the Reader terminal block. The chock goes nearest to the door/reader.  Example: Radio Shack part # 273-104 (2-pack) for $8.39. Diodes are provided with each APC or VertX System and the lack of one strapped across the Power wires to the Lock can also create strange/odd bits being displayed in the Event Manager. This occurs when a grounded strike allows feed-back current to travel back the control or sub-control boards (Especially APC hardware). The diode is installed in parallel across the positive and negative wires with the striped side of the diode connected to the positive wire at the lock side. Pleasing the diodes in the panel is not the most effective use for the diodes. They need to be at the lock in the field.