This could happen I think if you have a lot of content to index and it's not finished before it's time to be run again.  Say you have 100 full pages of text and it would normally take one hour to finish indexing your site but for some reason ends up taking one hour and ten minutes. 

The task gets added back into the schedule before it's completed and you get the duplicate error.

Go in as host unders host / schedule / view schedule history and check for errors there.  Also try increasing the time between runs of the search re-indexing.

Some time ago I asked WH4L if I was part of their web farm, and was assured that was not the case.  Of course, that may or may not be true.

Turning off the scheduler has stopped the error, but that doesn't fix the underlying cause.  Nor does it help when you want scheduled items to run.  The error has been a problem for others, not on WH4L, and it would be a great help to get a definitive answer/cause/remedy for the issue.

What steps would you do, if you had your lab?  Maybe by outlining your process for us, someone might be able to set up and  perform those steps and relay results to you for your input.

Thanks,

Rick