diff --git a/src/Server/ZB.MOM.WW.OtOpcUa.AdminUI/Uns/IUnsTreeService.cs b/src/Server/ZB.MOM.WW.OtOpcUa.AdminUI/Uns/IUnsTreeService.cs
index f75486f6..3bff22e0 100644
--- a/src/Server/ZB.MOM.WW.OtOpcUa.AdminUI/Uns/IUnsTreeService.cs
+++ b/src/Server/ZB.MOM.WW.OtOpcUa.AdminUI/Uns/IUnsTreeService.cs
@@ -375,7 +375,8 @@ public interface IUnsTreeService
     /// <param name="equipmentId">The owning equipment.</param>
     /// <param name="input">The operator-editable virtual-tag fields.</param>
     /// <param name="ct">A token to cancel the operation.</param>
-    /// <returns>Success, or one of the guard failures.</returns>
+    /// <returns>Success, or one of the guard failures; or if the chosen script uses the <c>{{equip}}</c>
+    /// token but the equipment has no derivable single tag base.</returns>
     Task<UnsMutationResult> CreateVirtualTagAsync(string equipmentId, VirtualTagInput input, CancellationToken ct = default);
 
     /// <summary>
@@ -389,7 +390,8 @@ public interface IUnsTreeService
     /// <param name="input">The new operator-editable virtual-tag fields.</param>
     /// <param name="rowVersion">The concurrency token the caller last read.</param>
     /// <param name="ct">A token to cancel the operation.</param>
-    /// <returns>Success, a missing-row failure, a guard failure, or a concurrency failure.</returns>
+    /// <returns>Success, a missing-row failure, a guard failure, or a concurrency failure; or if the
+    /// chosen script uses the <c>{{equip}}</c> token but the equipment has no derivable single tag base.</returns>
     Task<UnsMutationResult> UpdateVirtualTagAsync(string virtualTagId, VirtualTagInput input, byte[] rowVersion, CancellationToken ct = default);
 
     /// <summary>
diff --git a/src/Server/ZB.MOM.WW.OtOpcUa.AdminUI/Uns/UnsTreeService.cs b/src/Server/ZB.MOM.WW.OtOpcUa.AdminUI/Uns/UnsTreeService.cs
index f719f16f..8632ba13 100644
--- a/src/Server/ZB.MOM.WW.OtOpcUa.AdminUI/Uns/UnsTreeService.cs
+++ b/src/Server/ZB.MOM.WW.OtOpcUa.AdminUI/Uns/UnsTreeService.cs
@@ -908,12 +908,10 @@ public sealed class UnsTreeService(IDbContextFactory<OtOpcUaConfigDbContext> dbF
         var fullNames = configs.Select(TagConfigFullName.Extract);
         if (EquipmentScriptPaths.DeriveEquipmentBase(fullNames) is null)
         {
-            // NOTE: literal {{equip}} must survive — in a C# interpolated string `{{`/`}}`
-            // collapse to single braces, so keep the token text in a NON-interpolated segment.
             return new UnsMutationResult(false,
                 $"Equipment '{equipmentId}' has no single tag base, so the "
-                + "{{equip}} token can't be resolved. Add at least one driver tag under this "
-                + "equipment (all sharing one object prefix), or remove {{equip}} from the script.");
+                + $"{EquipmentScriptPaths.EquipToken} token can't be resolved. Add at least one driver tag under this "
+                + $"equipment (all sharing one object prefix), or remove {EquipmentScriptPaths.EquipToken} from the script.");
         }
         return null;
     }
diff --git a/tests/Server/ZB.MOM.WW.OtOpcUa.AdminUI.Tests/Uns/VirtualTagEquipTokenValidationTests.cs b/tests/Server/ZB.MOM.WW.OtOpcUa.AdminUI.Tests/Uns/VirtualTagEquipTokenValidationTests.cs
index 5fff5e3b..58922c56 100644
--- a/tests/Server/ZB.MOM.WW.OtOpcUa.AdminUI.Tests/Uns/VirtualTagEquipTokenValidationTests.cs
+++ b/tests/Server/ZB.MOM.WW.OtOpcUa.AdminUI.Tests/Uns/VirtualTagEquipTokenValidationTests.cs
@@ -138,6 +138,41 @@ public sealed class VirtualTagEquipTokenValidationTests
         result.Error.ShouldBeNull();
     }
 
+    /// <summary>
+    /// {{equip}} script + TWO driver tags whose FullNames have DIFFERENT object prefixes
+    /// (no single base can be derived) → create rejected, error names equipment + token.
+    /// </summary>
+    [Fact]
+    public async Task Create_equip_token_with_divergent_prefixes_rejected()
+    {
+        var (service, dbName) = Fresh();
+        Seed(dbName, EquipBaseScript, tagFullName: "TestMachine_001.X");
+        using (var db = UnsTreeTestDb.CreateNamed(dbName))
+        {
+            db.Tags.Add(new Tag
+            {
+                TagId = "TAG-2",
+                DriverInstanceId = "DRV-1",
+                EquipmentId = "EQ-1",
+                Name = "y",
+                DataType = "Float",
+                AccessLevel = TagAccessLevel.Read,
+                TagConfig = "{\"FullName\":\"DelmiaReceiver_001.Y\"}",
+            });
+            db.SaveChanges();
+        }
+
+        var result = await service.CreateVirtualTagAsync("EQ-1", Input());
+
+        result.Ok.ShouldBeFalse();
+        result.Error.ShouldNotBeNull();
+        result.Error.ShouldContain("EQ-1");
+        result.Error.ShouldContain("{{equip}}");
+
+        using var verifyDb = UnsTreeTestDb.CreateNamed(dbName);
+        verifyDb.VirtualTags.Any(v => v.VirtualTagId == "VTAG-1").ShouldBeFalse();
+    }
+
     // ----- Update -----
 
     /// <summary>{{equip}} script + a derivable base → update succeeds.</summary>