各位大虾帮忙看看这是什么错误：

Illegal access: this web application instance has been stopped already. Could not load com.mysql.jdbc.Messages. The eventual following stack trace is caused by an error thrown for debugging purposes as well as to attempt to terminate the thread which caused the illegal access, and has no functional impact.
java.lang.IllegalStateException
at org.apache.catalina.loader.WebappClassLoader.loadClass(WebappClassLoader.java:1241)
at org.apache.catalina.loader.WebappClassLoader.loadClass(WebappClassLoader.java:1201)
at java.lang.ClassLoader.loadClassInternal(ClassLoader.java:319)
at com.mysql.jdbc.CommunicationsException.<init>(CommunicationsException.java:180)
at com.mysql.jdbc.MysqlIO.send(MysqlIO.java:2723)
at com.mysql.jdbc.MysqlIO.quit(MysqlIO.java:1401)
at com.mysql.jdbc.Connection.realClose(Connection.java:4882)
at com.mysql.jdbc.Connection.cleanup(Connection.java:2062)
at com.mysql.jdbc.Connection.finalize(Connection.java:3369)
at java.lang.ref.Finalizer.invokeFinalizeMethod(Native Method)
at java.lang.ref.Finalizer.runFinalizer(Finalizer.java:83)
at java.lang.ref.Finalizer.access$100(Finalizer.java:14)
at java.lang.ref.Finalizer$FinalizerThread.run(Finalizer.java:160)

请帮帮忙，小弟感激不尽

服务器已经启动了，而且网站也可以访问，但就是在日记里面总是看见这个信息

是，是放在lib下的

那请问出现这种错误的原因可能有哪些？