如何修复libmysqlclient.15.dylib未加载导致的错误？

我已升级到Rails 2.2.2并安装了MySQL 2.7 gem,当我尝试运行迁移或启动服务器时看到此错误:

dlopen(/Library/Ruby/Gems/1.8/gems/mysql-2.7/lib/mysql.bundle, 9): Library not loaded: /usr/local/mysql/lib/mysql/libmysqlclient.15.dylib
Referenced from: /Library/Ruby/Gems/1.8/gems/mysql-2.7/lib/mysql.bundle
Reason: image not found - /Library/Ruby/Gems/1.8/gems/mysql-2.7/lib/mysql.bundle

有什么问题？