This is a word of warning more than a question, if you are using RIAServices with Custom ValidatorAttributes.
Here is the Senario, I was creating a custom DataAnnotation that would validate a property based on whether or not a possible series of other properties had been set, such as; if Prop1 was 100 then Prop2, Prop3, or Prop4 could not be 0 one of them had to be set. I am also using RIA Services so I created the ValidatorAttribute my .shared.cs file. After writing all the tests for the helper CannotBeZeroIf class, I began to add the attributes to the Model Class. This is of course when thing started to go very wrong. RIA Services began to throw up during the CodeGen, with a NullReferenceException.
CreateRiaClientFilesTask -> NullReferenceException
It turns out to be linked to the fact that I was using the validator's constructor to pass in the values to the class. By switching to using ObjectInitialization syntax, everything was fixed.
The Answer appears to be use ObjectInitializer syntax when dealing with RIA Services and Custom DataAnnotation Validators.