Unnamed

This is a problem with the ant setup in eclipse. You need to remove all reference to previous jdk. In my case I had to go to 
windows->preferences->ant->runtime and update Global Entries to point to jdk1.6.0_03z\lib\tools.jar. It had previously been pointing at jdk1.4.2_09\lib\tools.jar which is the version of java I was upgrading from.