Ant编译找不到包

    [javac] D:\workspace\avaworkspace\TRMS\src\com\smartone\sn\nsms\emailthread\CheckMailTimerTask.java:24: package javax.mail does not exist
    [javac] import javax.mail.BodyPart;
    [javac]                  ^
    [javac] D:\workspace\avaworkspace\TRMS\src\com\smartone\sn\nsms\emailthread\CheckMailTimerTask.java:25: package javax.mail does not exist
    [javac] import javax.mail.Folder;
    [javac]                  ^
    [javac] D:\workspace\avaworkspace\TRMS\src\com\smartone\sn\nsms\emailthread\CheckMailTimerTask.java:26: package javax.mail does not exist
    [javac] import javax.mail.Header;
    [javac]                  ^
    [javac] D:\workspace\avaworkspace\TRMS\src\com\smartone\sn\nsms\emailthread\CheckMailTimerTask.java:27: package javax.mail does not exist
    [javac] import javax.mail.Message;
    [javac]                  ^
    [javac] D:\workspace\avaworkspace\TRMS\src\com\smartone\sn\nsms\emailthread\CheckMailTimerTask.java:28: package javax.mail does not exist
    [javac] import javax.mail.MessagingException;
    [javac]                  ^
    [javac] D:\workspace\avaworkspace\TRMS\src\com\smartone\sn\nsms\emailthread\CheckMailTimerTask.java:29: package javax.mail does not exist
    [javac] import javax.mail.Multipart;
    [javac]                  ^
    [javac] D:\workspace\avaworkspace\TRMS\src\com\smartone\sn\nsms\emailthread\CheckMailTimerTask.java:30: package javax.mail does not exist
    [javac] import javax.mail.Part;
    [javac]                  ^
    [javac] D:\workspace\avaworkspace\TRMS\src\com\smartone\sn\nsms\emailthread\CheckMailTimerTask.java:31: package javax.mail does not exist
    [javac] import javax.mail.Session;
    [javac]                  ^
    [javac] D:\workspace\avaworkspace\TRMS\src\com\smartone\sn\nsms\emailthread\CheckMailTimerTask.java:32: package javax.mail does not exist
    [javac] import javax.mail.Store;
    [javac]                  ^
    [javac] D:\workspace\avaworkspace\TRMS\src\com\smartone\sn\nsms\emailthread\CheckMailTimerTask.java:33: package javax.mail.internet does not exist
    [javac] import javax.mail.internet.MimeMessage;当然这些包都能在WebContent\WEB-INF\lib找到
什么问题?