diff --git a/src/Server/ZB.MOM.WW.OtOpcUa.AdminUI/Components/Shared/Uns/EquipmentModal.razor b/src/Server/ZB.MOM.WW.OtOpcUa.AdminUI/Components/Shared/Uns/EquipmentModal.razor
index 810b4e0f..838a5e7a 100644
--- a/src/Server/ZB.MOM.WW.OtOpcUa.AdminUI/Components/Shared/Uns/EquipmentModal.razor
+++ b/src/Server/ZB.MOM.WW.OtOpcUa.AdminUI/Components/Shared/Uns/EquipmentModal.razor
@@ -12,7 +12,7 @@
 {
     <div class="modal-backdrop fade show" style="display:block"></div>
     <div class="modal fade show" tabindex="-1" role="dialog" style="display:block">
-        <div class="modal-dialog modal-lg" role="document">
+        <div class="modal-dialog modal-xl" role="document">
             <div class="modal-content">
                 <EditForm Model="_form" OnValidSubmit="SaveAsync" FormName="equipmentModal">
                     <DataAnnotationsValidator />
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 47278b61..1a819f1d 100644
--- a/src/Server/ZB.MOM.WW.OtOpcUa.AdminUI/Uns/UnsTreeService.cs
+++ b/src/Server/ZB.MOM.WW.OtOpcUa.AdminUI/Uns/UnsTreeService.cs
@@ -999,7 +999,12 @@ public sealed class UnsTreeService(IDbContextFactory<OtOpcUaConfigDbContext> dbF
             .Select(d => d.ClusterId)
             .FirstOrDefaultAsync(ct);
 
-        if (driverCluster is not null && driverCluster != lineCluster)
+        if (driverCluster is null)
+        {
+            return new UnsMutationResult(false, $"Driver '{input.DriverInstanceId}' not found.");
+        }
+
+        if (driverCluster != lineCluster)
         {
             return new UnsMutationResult(
                 false,
diff --git a/tests/Server/ZB.MOM.WW.OtOpcUa.AdminUI.Tests/Uns/UnsTreeServiceEquipmentTests.cs b/tests/Server/ZB.MOM.WW.OtOpcUa.AdminUI.Tests/Uns/UnsTreeServiceEquipmentTests.cs
index 9e2555d6..b5831e0a 100644
--- a/tests/Server/ZB.MOM.WW.OtOpcUa.AdminUI.Tests/Uns/UnsTreeServiceEquipmentTests.cs
+++ b/tests/Server/ZB.MOM.WW.OtOpcUa.AdminUI.Tests/Uns/UnsTreeServiceEquipmentTests.cs
@@ -192,6 +192,26 @@ public sealed class UnsTreeServiceEquipmentTests
         verify.Equipment.Any(e => e.MachineCode == "machine_001").ShouldBeFalse();
     }
 
+    /// <summary>Binding equipment to a DriverInstanceId that does not exist is blocked with a "not found" error.</summary>
+    [Fact]
+    public async Task CreateEquipment_driver_not_found_blocked()
+    {
+        var (service, dbName) = Fresh();
+        // Seed area + line in MAIN cluster, but NO DriverInstance.
+        SeedLineAndDriver(dbName, lineCluster: "MAIN", driverCluster: null);
+
+        var result = await service.CreateEquipmentAsync(
+            Input("machine-1", "machine_001", "LINE-1", "DRV-GHOST"));
+
+        result.Ok.ShouldBeFalse();
+        result.Error.ShouldNotBeNull();
+        result.Error.ShouldContain("not found");
+        result.Error.ShouldContain("DRV-GHOST");
+
+        using var db = UnsTreeTestDb.CreateNamed(dbName);
+        db.Equipment.Any(e => e.MachineCode == "machine_001").ShouldBeFalse();
+    }
+
     // ----- UpdateEquipment -----
 
     /// <summary>Updating equipment changes its mutable fields (name, MachineCode, a 40010 field).</summary>