Cause
This error occurs when an updating method is called for an operand that has a value that cannot be updated.
The operand can be a:
Property of the receiver object in a non-updating method
Constant parameter
Substring
Read-only primitive attribute
Action
Remove or correct the invalid method call.
If the operand is a property of the receiver and the current method is non-updating, resolve the error by making the current method updating.
If the operand is a constant parameter (the default), resolve the error by changing the parameter to input.
In some cases, it may be possible to change the method being called from updating to non-updating if it does not actually update the receiver.