In some custom functions, the parameter may have a drop down with a selection of year. If you have a dimension or member in your application named year, using the custom function with the selection of year will not validate. This could be an issue for any parameter selection (not just year) that is also a dimension or member name.
To work around this issue, after selecting year from the parameter’s drop down, in the rule, add
@name( ) around it, so that it shows as: