There have been reports of this issue before, but the v3 update was supposed to fix this problem...
For More Information see: FileMaker Server
This is one of many acknowledged bugs that can be found in the Known Bug List here in the Report an Issue section of the forum.
It can also be downloaded as a database file from: http://www.4shared.com/file/8orL8apk/FMP_Bugs.html
We are running the lastest and greatest....issues still there? Seems to be with the listener.