The act type theory of propositions holds that propositions are act types directed toward propositional constituents (whether objects and properties, or concepts). I here present a general objection, targeting at once Russellian and Fregean act-type theories, which trades on the fact that some sentences have alternative analyses. For instance, ”Mary loves John” can be seen both as the result of saturating ”loves John” with ”Mary” and as the result of saturating ”Mary loves” with ”John”. I argue that the idea of alternative analyses is non-negotiable, and furthermore that this fact, together with certain plausible identity conditions on act types, entails that any sentence with alternative analyses (in fact, any atomic sentence with a polyadic predicate) is ambiguous. This consequence is shown to be counterintuitive and a radical departure from standard semantic assumptions. I discuss various possible retreat positions for act-type theorists and argue that they all come with considerable problems and depart significantly from extant act-type theories.