Userservice and stringprep

When I tried to use UserService I get error Stringprep class not defined. I found stringprep.jar file on the openfire website, but I am not sure where to add this jar file so that UserService jar file will see this stringprep.jar file. I tried to add stringprep.jar as a plugin to openfire, but it did not work.

I appreciate your help in advance.

Thanks,

R2D2