[Ipopt] Problem installing java interface

[Edmund Noon]

I obtained the code using svn. I did remember to set JAVA_HOME.
make, make test and make install all ran fine.
But when I

cd Ipopt/contrib/JavaInterface
make

I get the following error :
/usr/lib/jvm/java-6-sun-1.6.0.16/bin/javah -jni `echo 
org/coinor/Ipopt.class | sed -e 's|/|.|g' -e 's|.class||'`
error: cannot access org.coinor.Ipopt
class file for org.coinor.Ipopt not found
javadoc: error - Class org.coinor.Ipopt not found.
Error: No classes were specified on the command line.  Try -help.
make: *** [org_coinor_Ipopt.h] Error 15

I am using sun java 1.6.0.16 and ubuntu 9.04.

Has anyone got any ideas what I am doing wrong?