TFS Build fails to copy to drop location

Building my 开发者_运维百科solution succeeds, but the build fails upon copying from the build to the drop location. I get an error like this

TF270002: An error occurred copying files from 'E:\Workspace' to '\\server\drop location_20101026.25'. 
Details: Access to the path '\\server\drop location_20101026.25\_PublishedWebsites\website\bin\somecompiled.dll' is denied.

This is a part of a continuous integration build (as well as several other types of build that I've tried). This is a copied build definition from a definition that has worked for several months now, running on TFS 2010.

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Yep, I was right, I did this myself by putting the copy to drop location task in the parallel foreach loop, resulting in the task being done 3 times, and causing my problems.