Datamapper do_postgres gem error: "dyld: lazy symbol binding failed: Symbol not found: _PQsetdbLogin"

I'm trying to run a Sinatra application with Datamapper and a Postgres db locally. I'm on Mac OS X 10.6.7 and ruby 1.9.2 and each time I launch the application, I get the following error:

dyld: lazy symbol binding failed: Symbol not found: _开发者_运维百科PQsetdbLogin
    Referenced from: /ruby-1.9.2-p136/gems/do_postgres-0.10.5/lib/do_postgres/do_postgres.bundle
    Expected in: flat namespace

Does anybody have any idea why such an error?

Thanks a lot

---

probably you use a different version of libpq library than ruby driver expected. Check a version of libpq.

Pavel