diff --git a/TSG/Update/Known-Issue-Solution-update-fails-at-RegisterCloudManagementClusterExtensions-with-connection-refused.md b/TSG/Update/Known-Issue-Solution-update-fails-at-RegisterCloudManagementClusterExtensions-with-connection-refused.md
new file mode 100644
index 00000000..d32ab0e3
--- /dev/null
+++ b/TSG/Update/Known-Issue-Solution-update-fails-at-RegisterCloudManagementClusterExtensions-with-connection-refused.md
@@ -0,0 +1,139 @@
+# Symptoms
+
+A solution update fails at **RegisterCloudManagementClusterExtensions** with a connection error to
+port 42545. Virtual machines and storage are unaffected, but the update does not continue.
+
+```text
+Type 'RegisterCloudManagementClusterExtensions' of Role 'CloudManagementConfig' raised an exception:
+Exception occurred in Get-ClusterExtension: System.Net.WebException: Unable to connect to the remote server
+ ---> System.Net.Sockets.SocketException: No connection could be made because the target machine
+      actively refused it <node-ip-address>:42545
+```
+
+The same failure sometimes appears as a timeout instead:
+
+```text
+System.Net.Sockets.SocketException: A connection attempt failed because the connected party did not
+properly respond after a period of time <node-ip-address>:42545
+```
+
+The Azure Local host service (HciSvc) has crashed on at least one node. Its Application log records:
+
+* **Event ID 1026** from `.NET Runtime` — `HciSvc.exe` terminated by an unhandled `System.AccessViolationException`
+* **Event ID 1000** from `Application Error` — `HciSvc.exe` faulted with exception code `0xc0000005`
+
+# Issue Validation
+
+Run this from any node. It checks every node for HciSvc crashes since that node last restarted.
+
+```powershell
+Invoke-Command (Get-ClusterNode) {
+    $boot = (Get-CimInstance Win32_OperatingSystem).LastBootUpTime
+    Get-WinEvent -FilterHashtable @{LogName='Application'; Id=1000,1026; StartTime=$boot} -ErrorAction SilentlyContinue |
+        Where-Object Message -match 'HciSvc' | Select-Object -First 2
+} | Format-List PSComputerName, TimeCreated, Id, Message
+```
+
+An affected node returns entries like these:
+
+```text
+PSComputerName : NODE01
+TimeCreated    : 9/2/2026 8:58:08 PM
+Id             : 1026
+Message        : Application: HciSvc.exe
+                 Framework Version: v4.0.30319
+                 Description: The process was terminated due to an unhandled exception.
+                 Exception Info: System.AccessViolationException
+                    at Microsoft.AzureStack.HCI.Interop.En.ID(IntPtr, UInt32 ByRef, IntPtr, UInt32 ByRef, UInt32, UInt32)
+                    at Microsoft.AzureStack.HCI.Enclave.HciEnclave+EnclaveClient.EnclaveImdsOp(EnclaveImdsFunction, Byte[], Byte[])
+                    at Microsoft.AzureStack.HCI.Enclave.HciEnclave.ImdsSign(Byte[], Byte[])
+                    at Microsoft.AzureStack.HCI.Imds.ImdsAttestationCommon.SignAttestedData(Microsoft.AzureStack.HCI.Imds.AttestedData)
+
+PSComputerName : NODE01
+TimeCreated    : 9/2/2026 8:58:09 PM
+Id             : 1000
+Message        : Faulting application name: HciSvc.exe, version: 10.0.26100.33296, time stamp: 0x90103505
+                 Faulting module name: ucrtbase.dll, version: 10.0.26100.33158, time stamp: 0x32c000ad
+                 Exception code: 0xc0000005
+                 Fault offset: 0x00000000000edb0b
+                 Faulting application path: C:\Windows\system32\azshci\HciSvc.exe
+```
+
+Any entries returned confirm this issue. Nothing returned on any node means the update failed for
+another reason.
+
+If the update error says **BadRequest** rather than a connection failure to port 42545, this article
+does not apply.
+
+# Cause
+
+A virtualization-based security (VBS) key rotation leaves HciSvc holding a stale key. HciSvc fails
+when it next uses that key, and the service crashes. The Cloud Management service depends on HciSvc,
+so it cannot start, and the extension registration step has nothing to connect to.
+
+Restarting the service on its own does not clear it. The key is renewed when the cluster
+registration is re-synced.
+
+Azure Local 2609 detects and recovers this automatically during the solution update. On earlier
+versions, use the steps below.
+
+# Mitigation Details
+
+Run from one node in an elevated PowerShell session.
+
+```powershell
+# 1. Start HciSvc wherever it is stopped.
+Invoke-Command (Get-ClusterNode) {
+    if ((Get-Service HciSvc).Status -ne 'Running') { Start-Service HciSvc }
+}
+
+# 2. Re-sync the cluster registration. This renews the key.
+$before = (Get-AzureStackHCI).LastConnected
+Sync-AzureStackHCI
+
+# Sync-AzureStackHCI returns nothing and does not wait, so watch LastConnected instead.
+# Allow longer than 5 minutes on large clusters, roughly 16 nodes or more.
+$deadline = (Get-Date).AddMinutes(5)
+while ((Get-Date) -lt $deadline) {
+    Start-Sleep -Seconds 20
+    $now = (Get-AzureStackHCI).LastConnected
+    if ($now -and (-not $before -or $now -gt $before)) { "Sync completed at $now"; break }
+    "Waiting for sync to complete..."
+}
+
+# 3. Bring the Cloud Management role back online if it did not recover on its own.
+$group = Get-ClusterGroup -Name 'Cloud Management' -ErrorAction SilentlyContinue
+if ($group -and $group.State -ne 'Online') {
+    Stop-ClusterGroup  -Name 'Cloud Management' -Wait 60
+    Start-ClusterGroup -Name 'Cloud Management' -Wait 60
+}
+```
+
+Confirm every node can sign again without crashing:
+
+```powershell
+Invoke-Command (Get-ClusterNode) {
+    $uri = "http://127.0.0.1:42542/metadata/attested/document?api-version=2021-02-01&nonce=$(Get-Random)"
+    [pscustomobject]@{
+        Node   = $env:COMPUTERNAME
+        Status = (Invoke-WebRequest -Uri $uri -Headers @{Metadata='true'} -UseBasicParsing -TimeoutSec 60).StatusCode
+    }
+} | Format-Table Node, Status -AutoSize
+```
+
+```text
+Node   Status
+----   ------
+NODE01    200
+NODE02    200
+NODE03    200
+```
+
+A status of `200` from every node means the signing path works. If HciSvc were still failing there
+would be no response at all.
+
+Then retry the update or other operation you were running.
+
+If HciSvc is still crashing, run the steps above once more. A second pass sometimes clears the
+remaining nodes. If the operation still fails after that, collect diagnostic data with
+`Send-DiagnosticData` and open a support case.
diff --git a/TSG/Update/README.md b/TSG/Update/README.md
index f9f3f04e..040b56b1 100644
--- a/TSG/Update/README.md
+++ b/TSG/Update/README.md
@@ -37,3 +37,4 @@
 * [Update fails due to Arc Agent install failure (lockdown on azcmagent.log)](./Update-fails-due-to-Arc-Agent-install-failure.md)
 * [2604 | Previous CAU run status was canceled](./Previous-CAU-run-status-was-canceled.md)
 * [Live migration fails with "No mapping between account names and security IDs" (0x80070534)](./Live-migration-fails-with-No-mapping-between-account-names-and-security-IDs.md)
+* [Solution update fails at RegisterCloudManagementClusterExtensions with connection refused on port 42545](./Known-Issue-Solution-update-fails-at-RegisterCloudManagementClusterExtensions-with-connection-refused.md)