java.lang.LinkageError: Class violates loader constraints

[sk]

Hi all. I have next problem:

i create two eclipse plugin and attach to either of them one (the
same) external jar file (i want use it like external library). If i
invoke some method from this jar - it's work perfect. However, if i
try transfer any class instance (created in jar) from plugin A to
plugin B i get the following error...
java.lang.LinkageError: Class com/xprom/kernel_proxy/
KernelProxy violates loader constraints

How i understand - this error to result work two another classloaders
with my plugins, because they use different classpath but i don't
understand how it fixed!

Somebody confronted with similar problem?
Thanks in advance.