What's the manifest for the classpath for the jar? Is it an absolute path (offhand I'm thinking that this *has* to be relative, but can't recall if the jar will build on an absolute)?
It looks like it simply can't find it which would be the case if the classpath isn't absolute (which I'm thinking it can't be) and the actual CLASSPATH doesn't include the path to this linked jar. If it looks good, I'd try moving your jar to anywhere on C that is not the original location (if it existed), and is not in a system path and see if that goes. If that goes, its possible that this is a security issue across the volumes.