Tomcat 5 Wierdness

I've just installed Tomcat 5 on a SuSE 9.3 box. Admin and sample apps
seem to run O.K., but when I deploy a (previously-working) app I get

org.apache.jasper.JasperException: Unable to compile class for JSP

errors thrown, as if it can't find the app's WEB-INF/classes
directory. Needless to say, the directory is there and the necessary
classes are present in it.

Did I mention that this app is currently working properly on a old
Tomcat 3 server on a Red Hat 7.3 box? Oh, yeah, I did...

I'm sure I missed something along the way, but I am at a loss to say
what. I've RTFM'd until I'm cross-eyed, but I need to buy a clue.

Anyone with a suggestion that moves me out of my current impasse will
earn my eternal gratitude.