Creating a Web Application with Ant and Tomcat 4
Subject:   Build Failed ...
Date:   2004-12-21 14:18:23
From:   nt_yng
Response to: Build Failed ...

In your file make sure you double escape your path separators.
C:\tomcat\common\lib should be C:\\tomcat\\common\\lib.

That's why you didn't get a slash in the error message, Ant read it as an escape character.