The problem is not with the use of DSL sentences but with the use of 'mvel'
dialect. It appears that Mvel doesn't like the throw Exception syntax.
The solution is to use 'java'
dialect instead.
In order to do that, you must add 'java'
dialect option in your rule:
Unfortunately, as far as I remember, there is no global setting in Guvnor to use 'java'
dialect by default.