diff --git a/CDP4Orm/CDP4Orm.csproj b/CDP4Orm/CDP4Orm.csproj
index 6fac5c22..8d858445 100644
--- a/CDP4Orm/CDP4Orm.csproj
+++ b/CDP4Orm/CDP4Orm.csproj
@@ -80,7 +80,7 @@
   </ItemGroup>
 
   <ItemGroup>
-    <PackageReference Include="CDP4JsonSerializer-CE" Version="27.0.2" />
+    <PackageReference Include="CDP4JsonSerializer-CE" Version="27.1.0" />
     <PackageReference Include="Npgsql" Version="8.0.3" />
     <PackageReference Include="Microsoft.Extensions.Logging.Abstractions" Version="8.0.1" />
   </ItemGroup>
diff --git a/CometServer/CometServer.csproj b/CometServer/CometServer.csproj
index 41c61fab..05782635 100644
--- a/CometServer/CometServer.csproj
+++ b/CometServer/CometServer.csproj
@@ -19,8 +19,8 @@
   <ItemGroup>
     <PackageReference Include="Autofac.Extensions.DependencyInjection" Version="9.0.0" />
     <PackageReference Include="Carter" Version="8.2.1" />
-    <PackageReference Include="CDP4MessagePackSerializer-CE" Version="27.0.2" />
-    <PackageReference Include="CDP4ServicesMessaging-CE" Version="27.0.2" />
+    <PackageReference Include="CDP4MessagePackSerializer-CE" Version="27.1.0" />
+    <PackageReference Include="CDP4ServicesMessaging-CE" Version="27.1.0" />
     <PackageReference Include="FluentValidation" Version="11.9.2" />
     <PackageReference Include="Microsoft.AspNetCore.Authentication.Negotiate" Version="8.0.6" />
     <PackageReference Include="Microsoft.Extensions.Caching.Memory" Version="8.0.0" />
diff --git a/CometServer/Modules/10-25/ApiBase.cs b/CometServer/Modules/10-25/ApiBase.cs
index aa29471d..3b96a7cb 100644
--- a/CometServer/Modules/10-25/ApiBase.cs
+++ b/CometServer/Modules/10-25/ApiBase.cs
@@ -1047,5 +1047,24 @@ protected CometTask CreateAndRegisterCometTask(Guid actor, string topContainerNa
 
             return cometTask;
         }
+
+        /// <summary>
+        /// Adds a specific CDP error tag to an <see cref="HttpResponse"/> message
+        /// </summary>
+        /// <param name="httpResponse">The <see cref="HttpResponse"/></param>
+        /// <param name="errorTag">The the Error tag</param>
+        protected void AddErrorTagHeader(HttpResponse httpResponse, string errorTag)
+        {
+            var errorTagHeader = HttpConstants.CDPErrorTag;
+
+            if (!httpResponse.Headers.ContainsKey(errorTagHeader))
+            {
+                httpResponse.Headers[errorTagHeader] = errorTag;
+            }
+            else
+            {
+                httpResponse.Headers.TryAdd(errorTagHeader, errorTag);
+            }
+        }
     }
 }
diff --git a/CometServer/Modules/10-25/EngineeringModelApi.cs b/CometServer/Modules/10-25/EngineeringModelApi.cs
index 63057f7d..cccf4d43 100644
--- a/CometServer/Modules/10-25/EngineeringModelApi.cs
+++ b/CometServer/Modules/10-25/EngineeringModelApi.cs
@@ -1027,7 +1027,9 @@ protected async Task PostResponseData(PostRequestData postRequestData, string re
 
                     if (!IsPostAllowedOnIterationSetup(resourceProcessor, iteration))
                     {
-                        throw new Cdp4ModelValidationException($"It is not allowed to write data to a Frozen {nameof(IterationSetup)}, or its full containment tree. (#FROZEN_ITERATION).");
+                        this.AddErrorTagHeader(httpResponse, "#FROZEN_ITERATION");
+
+                        throw new Cdp4ModelValidationException($"It is not allowed to write data to a Frozen {nameof(IterationSetup)}, or its full containment tree.");
                     }
 
                     credentialsService.Credentials.Iteration = iteration;
diff --git a/CometServer/Services/Headers/HttpConstants.cs b/CometServer/Services/Headers/HttpConstants.cs
index 0707eb62..ef54d6ad 100644
--- a/CometServer/Services/Headers/HttpConstants.cs
+++ b/CometServer/Services/Headers/HttpConstants.cs
@@ -84,6 +84,11 @@ public static class HttpConstants
         /// </summary>
         public static readonly string AcceptCdpVersionHeader = "Accept-CDP";
 
+        /// <summary>
+        /// The header that specifies the the error tag of an http response message
+        /// </summary>
+        public static readonly string CDPErrorTag = "CDP-Error-Tag";
+
         /// <summary>
         /// The default data model version.
         /// </summary>