Two possible reason as what causing this issue:
- When a sampler was defined twice in Manage Entity, either in type or sampler itself.
- When a netprobe running in a machine having with two hostname resolving in one IP address. You may want to refer to gateway.log and look for this kind of entry:
<Sun Feb 15 12:14:34> INFO: HOSTRESOLVER host hostname1.domain.com resolved to 184.108.40.206