When the system boots up, especially in older MPC systems, you may see a scrambled alpha/numeric readout (A-Z,1-9) on the display, before the system progresses to the main screen. If the system does not begin normal operation and the message remains, you likely have a connection issue, or a short at one of your sensors.
A good start is to give your wiring a once over and see if something is be corroded, badly worn, or unplugged, as that would be the easiest and most likely solution.
If you don’t see anything obvious, then access your MPC board and unplug/unscrew everything besides the input voltage on the pegs, your display cable, and salinity probe (remove all other green pin plugs and any signal wires.)
Turn the system off and on again. If you still have the "Alphabet Soup" readout, than the issue is likely with your display panel, display cable or potentially the MPC board itself.
Upon restart if the message is gone and you get something other than "Alphabet Soup", turn the system off, add on one of the signal plugs or wires, and look again for the fault. If it does not come on, then continue with each plug/wire until you find the one with the issues. Then you know what wires to chase - or to look at a wiring diagram to find out what sensor might be giving you the issue.
With this issue, if the problem is not with the MPC board itself, it is most likely at a pressure transducer (sensor) or Rotoflo product flow meter. You can also try the alternate display port on the MPC board. If you have multiple displays, trade displays and see if the problem stays or follows the display panel.