Problems in scheduling a service for cluster

Hi
We have a clustered environment with two integration servers(webM 4.6) running in a cluster.
I want scheduled service that runs fine on individual b2b servers.But when i make the same service to run in cluster the scheduler on IS shows -ve value under the Next run column.Has any one faced such an issue before? what is possible cause and a possible solution.Any help will be appreciated a lot
Regards
Yogesh