rfacebook http 500 error

hey, here's my problem: I have a working rails application and everytime I install the rfacebook plugin (nothing more than running script/pluin install) all I get from the app is http 500s. I also did rake facebook:setup and it didnt help. Nothing goes to the logs file so I have no idea where to start... and of course once I delete the plugin dir the app comes back to life.

anyone ? thnx alot...