AssemblyInfoTask An item with the same key has already been added error

Target UpdateAssemblyInfoFiles:

C:\Program Files\MSBuild\Microsoft\AssemblyInfoTask\Microsoft.VersionNumber.Targets(90,5): error MSB4018: The "AssemblyInfo" task failed unexpectedly.

C:\Program Files\MSBuild\Microsoft\AssemblyInfoTask\Microsoft.VersionNumber.Targets(90,5): error MSB4018: System.ArgumentException: An item with the same key has already been added.

C:\Program Files\MSBuild\Microsoft\AssemblyInfoTask\Microsoft.VersionNumber.Targets(90,5): error MSB4018: at System.ThrowHelper.ThrowArgumentException(ExceptionResource resource)

C:\Program Files\MSBuild\Microsoft\AssemblyInfoTask\Microsoft.VersionNumber.Targets(90,5): error MSB4018: at System.Collections.Generic.Dictionary`2.Insert(TKey key, TValue value, Boolean add)

C:\Program Files\MSBuild\Microsoft\AssemblyInfoTask\Microsoft.VersionNumber.Targets(90,5): error MSB4018: at Microsoft.Build.Extras.AssemblyInfoWrapper..ctor(String filename)

C:\Program Files\MSBuild\Microsoft\AssemblyInfoTask\Microsoft.VersionNumber.Targets(90,5): error MSB4018: at Microsoft.Build.Extras.AssemblyInfo.Execute()

C:\Program Files\MSBuild\Microsoft\AssemblyInfoTask\Microsoft.VersionNumber.Targets(90,5): error MSB4018: at Microsoft.Build.BuildEngine.TaskEngine.ExecuteTask(ExecutionMode howToExecuteTask, Hashtable projectItemsAvailableToTask, BuildPropertyGroup projectPropertiesAvailableToTask, Boolean& taskClassWasFound)

Done building target "UpdateAssemblyInfoFiles" in project "TFSBuild.proj" -- FAILED.

Assemblyinfo looks like this

using System;

using System.Reflection;

using System.Security.Permissions;

using System.Runtime.InteropServices;

[assembly:AssemblyKeyName("")]

[assembly:AssemblyTitle("removed")]

[assembly:AssemblyProduct("removed")]

[assembly:AssemblyDescription("removed")]

[assembly:AssemblyCopyright("?removed")]

[assembly:CLSCompliant(false)]

[assembly:AssemblyVersion("1.0.0.0")]

[assembly:AssemblyFileVersion("1.0.0.0")]

[assembly:PermissionSet(SecurityAction.RequestMinimum, Name ="FullTrust")]

[assembly:PermissionSet(SecurityAction.RequestOptional, Name ="Nothing")]

[assembly:ComVisible(false)]

my build file is set up as in this post:http://blogs.msdn.com/gautamg/archive/2006/01/04/509146.aspx

Any ideas?

Mike