ArgumentOutOfRangeException on Data Download

twhitvine[CodePlex]
I was following the Elbe Precipitation tutorial from the Documentation page. I was downloading precip data for all sites when I got this error.

System.ArgumentOutOfRangeException: Index was out of range. Must be non-negative and less than the size of the collection.

Parameter name: index
at System.Collections.Generic.List`1.get_Item(Int32 index)
at HydroDesktop.DataDownload.Downloading.DownloadManager.DoDownload(Object state) in g:\TeamCity\buildAgent\work\e54ee16d10a0068\Source\DataDownload\DataDownload\Downloading\DownloadManager.cs:line 374

at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean ignoreSyncCtx)

at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state)

at System.Threading.ThreadHelper.ThreadStart(Object obj)

Start in Source\DataDownload\DataDownload\Downloading\DownloadManager.cs at line 374 and reproduce the Elbe Precipitation tutorial's download for all sites. Trace which collection access raises the exception, then verify that the all-sites download completes without the ArgumentOutOfRangeException.

Written by the indexing model from the issue text.