That class uses some classes from java.awt (http://svn.rhq-project.org/repos/rhq/trunk/modules/enterprise/gui/portal-war/src/main/java/org/rhq/enterprise/gui/image/chart/HighLowChart.java).
As a wild guess - are those classes present in your JVM?
Thanks for your replies....
I changed the JAVA home for jopr agent and server to jdk1.6
also there were two instances of jopr running on the machine
the charts are now working and the agent has gone form using 30-40% mem to 5%
server is running at 18%
I havent tried swithing java versions back to see if the high mem usage was because of the java version or because of the two jopr server process' running though