Just use a property for the release notes file.

Author: spraints

GitTfsTasks/CreateRelease.cs

@@ -40,7 +40,7 @@ public class CreateRelease : Task
 
         public ITaskItem[] Files { get; set; }
 
-        public ITaskItem ReleaseNotesFile { get; set; }
+        public string ReleaseNotesFile { get; set; }
 
         [Output]
         public ITaskItem[] UploadedAssets { get; private set; }
@@ -90,7 +90,7 @@ private ReleaseUpdate BuildReleaseData()
             var release = new ReleaseUpdate(TagName);
             if (ReleaseNotesFile != null)
             {
-                release.Description = File.ReadAllText(ReleaseNotesFile.ItemSpec);
+                release.Description = File.ReadAllText(ReleaseNotesFile);
             }
             return release;
         }

release.proj

@@ -94,11 +94,8 @@
   </Target>
 
   <!-- Internal: Called by Release to create the release on github.com. -->
-  <ItemGroup>
-    <ReleaseNotes Condition="'$(ReleaseNotes)' != ''" Include="$(ReleaseNotes)" />
-  </ItemGroup>
   <Target Name="UploadToGitHub" DependsOnTargets="VersionRequired; AuthTokenRequired; GitTfsTasks">
-    <CreateRelease Repository="git-tfs/msbuild-tasks" OauthToken="$(GitHubAuthToken)" TagName="$(VersionTag)" Files="@(ArchiveFile)" ReleaseNotesFile="@(ReleaseNotes)">
+    <CreateRelease Repository="git-tfs/msbuild-tasks" OauthToken="$(GitHubAuthToken)" TagName="$(VersionTag)" Files="@(ArchiveFile)" ReleaseNotesFile="$(ReleaseNotes)">
       <Output TaskParameter="UploadedAssets" ItemName="UploadedAssets" />
     </CreateRelease>
     <Message Text="yes! -> @(UploadedAssets)" />