weblogic:bean is already undeployed

Hello everyone
I am calling a function from “struts action class” to bean. I am using weblogic 8.1 web server.i am able to call the function from action class,when i restart the server.But when i redeploy the .ear from weblogic ,i am getting error.

java.rmi.NoSuchObjectException: Bean is already undeployed.

i am not able to solve the problem.

Waiting for reply..
Thanks