This error occurs if you're comparing an enumerated parameter with string value using the == or != operators, and the string value is not a valid option for the enumerated parameter.
Example:
if @myParam == "Howdy" ; "Howdy" is not a valid option
...
default:
int param myParam
enum = "Hello" "Goodbye"
default = 0
endparam
See Also
enum setting
Errors