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 r2131035a027.svr.emea.jpmchase.net resolved to 188.8.131.52