Weird ClassNotFoundException problem with Apache Tomcat

[Albretch]

I am trying to use hsqldb 1.7.1 as DBStore for sessions with Apache
Tomcat/4.1.24 running on W2K with the jdk.
Java(TM) 2 Runtime Environment, Standard Edition (build 1.4.1_02-b06)
Java HotSpot(TM) Client VM (build 1.4.1_02-b06, mixed mode)

I placed the HSQL jar, hsqldb.jar, in: %CATALINA_HOME%\shared\lib

but I keep getting

.... JDBCStore[/...]: JDBC driver class not found
java.lang.ClassNotFoundException: org.hsqldb.jdbcDriver

Is TC not supposed to be able to read jar libraries placed in
%CATALINA_HOME%\shared\lib by itself?

I can see the class org.hsqldb.jdbcDriver jared in there.

What could be possibly going on here?