Then look at http://support.asternic.biz on the article on how to debug FOP2, start capturing debug on the server and inspect the logs after you attempt such a transfer. You have FOP2 or Asterisk misconfigured, you will have to find out wher... the logs will give you strong hints about that.
Comments
If you are on a call, then select the target extension button and then the blind transfer action button at the top. What happens if you do that?
Best regards,