The "Illegal word operand Access" error can present itself due to application logic error or due to EMI. (electromagnetic interference)
Please follow next steps to help you determine the issue.
For example: Error code `42C`
If the error is at random and it's different all the time then it is highly possible that is cause by and external factor such as EMI, in this case please refer to the link below about "Wiring Guidelines".
http://www.unitronicsplc.com/Download/SoftwareUtilities/General_Wiring_Guidelines.pdf
If the LDR error is the same all the time, you may determine the subroutine that is implicated in this error by following the next steps:
This will point you to the suspected subroutine.