[plt-scheme] problem with match.ss and contracts

I'm using match.ss and contracts, and getting the following very strange 
error:

procedure application: expected procedure, given: 
#<struct:flat-contract>; arguments were: ()

On a bit of code that looks like this:

(match-lambda*
       [(...... (? string? key) ......) ....]

The ...... are not match ..., but just irrelevant code.

Can I not use regular predicates in match with contracts?

This bit of code is not in a define/contract, btw.

sam th