What to check

The red LED flashes indicating a communication problem between the reader and PinNet controller. 

Corrective Action

Check PinNet controller power voltage and reader L1-L6 connections

To prove it's not a wiring fault, wire the reader on a short piece of cable directly to the PinNet controller.

To check that the port on the PinNet controller is not at fault, wire the reader into a different port.

If the reader is a significant distance from the controller there may well be voltage drop and this can be solved by doubling up using spare conductors.

L1    +12v DC
L2    -12v DC
L3    TX data L2 --- L3 0.5v AC
L4    TX data L2 --- L4 8.7v AC
L5    RX data L2 --- L5 2.0v AC
L6    RX data L2 --- L6 5.8v AC

Links

https://www.entryphone.co.uk/pdf/PinNetManualV5.pdf