I recieved an internal error initalizing expression and I am not sure how to fix it

[AngelaMiddleton]

The error came after I created parameters for my model layout. The error is with my PCTUNDER18 clause. I am not sure how to go in and edit the clause.

[LanceCole1]

Angela, 

Can an you please provide more information such as a copy of the clause that is resulting in the error? Where specifically the error is occurring?  And copy of the error message? Etc.