diff --git a/code-reviews/Driver.Historian.Wonderware/findings.md b/code-reviews/Driver.Historian.Wonderware/findings.md
index cb7b4d4..86c70d1 100644
--- a/code-reviews/Driver.Historian.Wonderware/findings.md
+++ b/code-reviews/Driver.Historian.Wonderware/findings.md
@@ -7,7 +7,7 @@
 | Review date | 2026-05-22 |
 | Commit reviewed | `76d35d1` |
 | Status | Reviewed |
-| Open findings | 12 |
+| Open findings | 11 |
 
 ## Checklist coverage
 
@@ -36,7 +36,7 @@ a category produced nothing rather than leaving it blank.
 | Severity | High |
 | Category | Correctness and logic bugs |
 | Location | `Backend/SdkAlarmHistorianWriteBackend.cs:68`, `Backend/AahClientManagedAlarmEventWriter.cs:82-103` |
-| Status | Open |
+| Status | Resolved |
 
 **Description:** `MalformedErrors` includes `HistorianAccessError.ErrorValue.WriteToReadOnlyFile`.
 When `ClassifyOutcome` routes that code through `MapOutcome`, `isMalformedInput` is
@@ -54,7 +54,7 @@ be treated as a connection-class error (abort the batch, reset the connection so
 the reconnect path can re-open with `ReadOnly = false`) or at minimum as
 `RetryPlease`, never `PermanentFail`.
 
-**Resolution:** _(open)_
+**Resolution:** Resolved 2026-05-22 — moved `WriteToReadOnlyFile` from `MalformedErrors` into `ConnectionErrors` so the batch loop aborts, resets the connection (re-opening with `ReadOnly = false`), and defers the events as `RetryPlease` instead of dead-lettering them.
 
 ### Driver.Historian.Wonderware-002
 
diff --git a/src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Historian.Wonderware/Backend/SdkAlarmHistorianWriteBackend.cs b/src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Historian.Wonderware/Backend/SdkAlarmHistorianWriteBackend.cs
index 60b6184..738a82a 100644
--- a/src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Historian.Wonderware/Backend/SdkAlarmHistorianWriteBackend.cs
+++ b/src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Historian.Wonderware/Backend/SdkAlarmHistorianWriteBackend.cs
@@ -56,6 +56,13 @@ namespace ZB.MOM.WW.OtOpcUa.Driver.Historian.Wonderware.Backend
                 HistorianAccessError.ErrorValue.Stopping,
                 HistorianAccessError.ErrorValue.Win32Exception,
                 HistorianAccessError.ErrorValue.InvalidResponse,
+                // WriteToReadOnlyFile is a connection-configuration fault, not an event-payload
+                // fault: the session was opened without ReadOnly = false (a misconfiguration or
+                // a regression). The event itself is fine, so it must NOT be dead-lettered.
+                // Classifying it here aborts the batch and resets the connection so the
+                // reconnect path re-opens a writable (ReadOnly = false) session; the deferred
+                // events drain on the next tick. See Driver.Historian.Wonderware-001.
+                HistorianAccessError.ErrorValue.WriteToReadOnlyFile,
             };
 
         // ErrorValue codes that mean the event itself is malformed — permanent, never retried.
@@ -65,7 +72,6 @@ namespace ZB.MOM.WW.OtOpcUa.Driver.Historian.Wonderware.Backend
                 HistorianAccessError.ErrorValue.InvalidArgument,
                 HistorianAccessError.ErrorValue.ValidationFailed,
                 HistorianAccessError.ErrorValue.NullPointerArgument,
-                HistorianAccessError.ErrorValue.WriteToReadOnlyFile,
                 HistorianAccessError.ErrorValue.NotImplemented,
                 HistorianAccessError.ErrorValue.NotApplicable,
             };
diff --git a/tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Historian.Wonderware.Tests/Backend/SdkAlarmHistorianWriteBackendTests.cs b/tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Historian.Wonderware.Tests/Backend/SdkAlarmHistorianWriteBackendTests.cs
index 79b56fa..2be0944 100644
--- a/tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Historian.Wonderware.Tests/Backend/SdkAlarmHistorianWriteBackendTests.cs
+++ b/tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Historian.Wonderware.Tests/Backend/SdkAlarmHistorianWriteBackendTests.cs
@@ -96,7 +96,6 @@ namespace ZB.MOM.WW.OtOpcUa.Driver.Galaxy.Host.Tests
         [InlineData(HistorianAccessError.ErrorValue.InvalidArgument, AlarmHistorianWriteOutcome.PermanentFail)]
         [InlineData(HistorianAccessError.ErrorValue.ValidationFailed, AlarmHistorianWriteOutcome.PermanentFail)]
         [InlineData(HistorianAccessError.ErrorValue.NullPointerArgument, AlarmHistorianWriteOutcome.PermanentFail)]
-        [InlineData(HistorianAccessError.ErrorValue.WriteToReadOnlyFile, AlarmHistorianWriteOutcome.PermanentFail)]
         [InlineData(HistorianAccessError.ErrorValue.NotImplemented, AlarmHistorianWriteOutcome.PermanentFail)]
         public void ClassifyOutcome_maps_error_code_to_expected_outcome(
             HistorianAccessError.ErrorValue code, AlarmHistorianWriteOutcome expected)
@@ -104,6 +103,20 @@ namespace ZB.MOM.WW.OtOpcUa.Driver.Galaxy.Host.Tests
             SdkAlarmHistorianWriteBackend.ClassifyOutcome(code).ShouldBe(expected);
         }
 
+        [Fact]
+        public void ClassifyOutcome_WriteToReadOnlyFile_is_RetryPlease_not_PermanentFail()
+        {
+            // Driver.Historian.Wonderware-001 regression: WriteToReadOnlyFile is a
+            // connection-configuration fault (the write session was opened without
+            // ReadOnly = false), NOT a malformed-event fault. Routing it to PermanentFail
+            // would dead-letter every alarm event in the batch on a misconfigured/regressed
+            // connection — data loss. It must be treated as a transient connection-class
+            // error so the events are deferred and retried once the connection is corrected.
+            SdkAlarmHistorianWriteBackend.ClassifyOutcome(
+                    HistorianAccessError.ErrorValue.WriteToReadOnlyFile)
+                .ShouldBe(AlarmHistorianWriteOutcome.RetryPlease);
+        }
+
         // ── BuildConnectionArgs — read-only vs write shaping ──────────────────
 
         [Fact]