Security Exception when using org.eclipse.jdt.core plugin

I'm trying to use the org.eclipse.jdt.core jar from Eclipse in my Jazz ant build. I require this jar because it contains functionality to parse/navigate the bytecode of a class. When I try to execute my build using the JDT.core jar from my RTC client, I get the following exception:

build.xml:163: java.lang.SecurityException: class "org.eclipse.jdt.core.ToolFactory"'s signer information does not match signer information of other classes in the same package

Any ideas on how I can bypass this error?

Thanks