flow direction with streams error

[HeatherMcAdams]

I am trying to use the flow direction with streams function using an existing stream layer.  I am recieving the error message below.

System.NullReferenceException: Object reference not set to an instance of an object.
   at ESRI.APWR.ApHydro.ArcHydroOp.FlowDirectionWithStreams(ApLayers apLayers, Double stepsize, Double startElevation, ITrackCancel& trackcancel, IGPMessages& messages, String& exMessage)
System.NullReferenceException: Object reference not set to an instance of an object.
   at ESRI.APWR.ApHydro.ArcHydroOp.FlowDirectionWithStreams(ApLayers apLayers, Double stepsize, Double startElevation, ITrackCancel& trackcancel, IGPMessages& messages, String& exMessage)
Failed to execute (FlowDirectionWithStreams).
End Time: Thu Feb 23 07:44:33 2012 (Elapsed Time: 4.00 seconds)

My stream vector layer's attribute table does have flow direction 1 field and I created hydroID, from node to node, and next downID from the attribute tools.  Does anyone have any advice or info. for me?

Thanks,
Heather

[NicWarrens]

Heather,
Did you ever figure out the error? I'm having the exact same problem, and I would love to know how you fixed it.

Thanks!
Nic

[FernandoVasconcellos]

Hi

I'm having the same error! I found that a guy had the same error in 2009 and have answered himself, but I can't figure out what to do after reading him:

Subject Re: Flow direction with streams
Author Niall Duncan
Date Apr 15, 2009
Message As this is part of the toolbox rather than the toolbar you have to run the Create Target Locations tool before it will work. Could do with a slightly more helpful error message.

I'appreciate if anyone can explain me how this guy solved the problem or any other solution to the problem. Thanks