Hi Sam,
On the Omron 'K' series PLC's you have 5 minutes to change the battery. The 5 minutes includes removing the power, unscrewing the 4 screws, unplugging the battery, plugging the new battery in.
It sounds like the program, or part of it has been lost.
To change the fist line back on the Pro15.
Switch to program mode.
CLR Mon CLR
Arrow down
You should see the End(01) function on this line.
Enter the code that you noted above.
Example LD 1
Hit LD key and then the number key 1
Hit write
Place the switch back into run mode.
In order to check the program, you will need a copy or printout of the original program. Do you have anything available to you?
The memory error will occur when parts of the memory have been removed. I would first check to see if a program is in the unit. On the Pro15 do the following:
The Switch can be in any mode; Run, Mon or Program.
CLR Mon CLR
Use the down arrow. This will scroll through the program. At the end of the program you should have an END instruction.
This will be good to compare to the original program.
The instructions for the Pro15 are in the operation manual. Here is the link.
http://www.omronkft.hu/nostree/pdfs/plc/cxxk/w146e15_c20k_c28k_c40k_c60k_operation_manual.pdf
If you go to 4-6-5 Program Searches you can search for the END instruction.
Any mode.
CLR FUN 01 SRCH - This will search for the end statement
Hitting SRCH again will continue the search.
Regards,