diff --git a/playbook/shopfloor-setup/gea-shopfloor-cmm/scripts/gocmm-debug.bat b/playbook/shopfloor-setup/gea-shopfloor-cmm/scripts/gocmm-debug.bat
index aaf42bf..401d5f5 100644
--- a/playbook/shopfloor-setup/gea-shopfloor-cmm/scripts/gocmm-debug.bat
+++ b/playbook/shopfloor-setup/gea-shopfloor-cmm/scripts/gocmm-debug.bat
@@ -4,13 +4,16 @@ REM
 REM   *** RUN THIS AS THE OPERATOR (the locked-down shop-floor user). ***
 REM   *** DO NOT right-click "Run as administrator" - that hides the bug. ***
 REM
-REM Diagnoses two goCMM failures:
+REM Diagnoses goCMM startup failures:
 REM   1. "Requested registry access is not allowed" - dumps the goCMM key ACL
-REM      to confirm lockdown stripped the BUILTIN\Users write grant.
-REM   2. "Object reference not set to an instance of an object" at start -
-REM      PROBE 3 compares the registry 'Selected Part Group' against the
-REM      ApplicationSettings.xml part groups (case-sensitive) and names the
-REM      mismatch (host form / \shared vs \SHARED) that nulls SelectedPartGroup.
+REM      to confirm lockdown stripped the BUILTIN\Users write grant (PROBE 1-2).
+REM   2. "Object reference not set to an instance of an object" at start:
+REM      - PROBE 3: part-group match (reg vs ApplicationSettings.xml, case-sensitive).
+REM      - PROBE 4: pulls the actual .NET crash stack from the Application log.
+REM      - PROBE 5: part-group UNC reachability + PC-DMIS COM registration.
+REM      Confirmed root cause to date: PC-DMIS COM server NOT registered ->
+REM      goCMM's Activator.CreateInstance gets a null type -> NRE. Fix: run
+REM      Pcdlrn.exe once elevated (/regserver). PROBE 5 reports this directly.
 REM Output lands in C:\Logs\CMM\.
 
 setlocal
diff --git a/playbook/shopfloor-setup/gea-shopfloor-cmm/scripts/gocmm-debug.ps1 b/playbook/shopfloor-setup/gea-shopfloor-cmm/scripts/gocmm-debug.ps1
index e1b7419..20fa5cb 100644
--- a/playbook/shopfloor-setup/gea-shopfloor-cmm/scripts/gocmm-debug.ps1
+++ b/playbook/shopfloor-setup/gea-shopfloor-cmm/scripts/gocmm-debug.ps1
@@ -161,6 +161,87 @@ try {
 } catch { W "  ERROR in part-group probe: $($_.Exception.Message)" }
 W ""
 
+W "================ PROBE 4: goCMM crash events (Application log) - the actual stack ================"
+# The NRE reproduces even for admin, so it is NOT a rights problem. The faulting
+# stack names the null object. .NET pushes it to the Application log under
+# '.NET Runtime' / 'Application Error' / 'Windows Error Reporting'.
+try {
+    $since = (Get-Date).AddDays(-14)
+    $ev = Get-WinEvent -FilterHashtable @{ LogName='Application'; StartTime=$since } -ErrorAction SilentlyContinue |
+          Where-Object { $_.ProviderName -match '\.NET Runtime|Application Error|Windows Error Reporting|Application Hang' -and "$($_.Message)" -match 'goCMM' }
+    if (-not $ev) {
+        W "  (no goCMM-related crash events in the last 14 days - launch goCMM once, then re-run this)"
+    } else {
+        foreach ($e in ($ev | Select-Object -First 5)) {
+            W ("  ---- {0}  [{1}]  EventId={2} ----" -f $e.TimeCreated, $e.ProviderName, $e.Id)
+            foreach ($line in ("$($e.Message)" -split "`r?`n")) { W ("    " + $line) }
+            W ""
+        }
+        W "  >> The topmost goCMM / GEA_OFI frame in the stack above is where the null is dereferenced. <<"
+    }
+} catch { W "  ERROR reading event log: $($_.Exception.Message)" }
+W ""
+
+W "================ PROBE 5: part-group UNC reachability + PC-DMIS install ================"
+# (a) Can THIS bay open the Selected Part Group share? An unreachable / unauthenticated
+#     UNC -> goCMM enumerates null -> startup NRE, regardless of local rights (admin too).
+try {
+    $base32 = [Microsoft.Win32.RegistryKey]::OpenBaseKey('LocalMachine','Registry32')
+    $kpg = $base32.OpenSubKey($key32native, $false)
+    $pg = if ($kpg) { [string]$kpg.GetValue('Selected Part Group','') } else { '' }
+    if ($kpg) { $kpg.Close() }
+    if ($pg) {
+        W ("  part group UNC: $pg")
+        if (Test-Path -LiteralPath $pg -ErrorAction SilentlyContinue) {
+            $n = @(Get-ChildItem -LiteralPath $pg -ErrorAction SilentlyContinue).Count
+            W ("  >> REACHABLE - $n item(s) under it. (not the NRE cause) <<")
+        } else {
+            W "  >> *** UNREACHABLE *** bay cannot open the part-group UNC (share offline, not on the"
+            W "  >> production net yet, or no credential to \\tsgwp00525\SHARED). goCMM enumerating this"
+            W "  >> path returns null -> startup NRE even for admin. Check net connectivity + share auth. <<"
+        }
+    } else { W "  (no Selected Part Group in registry)" }
+} catch { W "  ERROR testing part-group UNC: $($_.Exception.Message)" }
+W ""
+# (b) PC-DMIS COM automation - THE confirmed root cause (see debug.log). goCMM
+#     connects via Activator.CreateInstance on the PC-DMIS COM type. If the
+#     automation server is not registered, Type.GetTypeFromProgID returns null
+#     -> CreateInstance(null) -> "ArgumentNullException: ... Parameter name: type"
+#     -> ConnectToSoftware derefs null -> NRE. PC-DMIS can be RUNNING and still
+#     not be COM-registered. Stack: GEAE.Common.CMM.CMMInterfaces.PCDMIS.ConnectToSoftware.
+$comOk = $false
+foreach ($pgid in 'PCDLRN.Application','PCDLRN.Automation','Pcdlrn.Application','PCDLRN.Object') {
+    foreach ($cls in "HKLM:\SOFTWARE\Classes\$pgid","HKLM:\SOFTWARE\Classes\WOW6432Node\$pgid") {
+        if (Test-Path $cls) {
+            $clsid = (Get-ItemProperty -Path "$cls\CLSID" -ErrorAction SilentlyContinue).'(default)'
+            $comOk = $true
+            $srv = $null
+            if ($clsid) {
+                foreach ($cb in "HKLM:\SOFTWARE\Classes\CLSID\$clsid\LocalServer32","HKLM:\SOFTWARE\Classes\WOW6432Node\CLSID\$clsid\LocalServer32") {
+                    if (Test-Path $cb) { $srv = (Get-ItemProperty -Path $cb -EA SilentlyContinue).'(default)' }
+                }
+            }
+            W ("  COM ProgID registered: $pgid  CLSID=$clsid  server=$srv")
+        }
+    }
+}
+if (-not $comOk) {
+    W "  >> *** PC-DMIS COM SERVER NOT REGISTERED *** no PCDLRN.* ProgID in HKCR. This is exactly the"
+    W "  >> null behind 'ArgumentNullException: ... Parameter name: type' in debug.log -> goCMM startup NRE."
+    W "  >> FIX: run the installed Pcdlrn.exe once ELEVATED (self-registers), or 'Pcdlrn.exe /regserver'."
+    W "  >> Then confirm the registered build matches the goCMM-expected PC-DMIS version (the version gate). <<"
+}
+# install presence (context for the COM verdict)
+$pcdlrn = $null
+foreach ($d in 'C:\Program Files\Hexagon','C:\Program Files (x86)\Hexagon','C:\Program Files\WAI','C:\Program Files (x86)\WAI') {
+    if (Test-Path $d) {
+        $hit = Get-ChildItem $d -Filter 'Pcdlrn.exe' -Recurse -ErrorAction SilentlyContinue | Select-Object -First 1
+        if ($hit) { $pcdlrn = $hit.FullName; W ("  Pcdlrn.exe: $($hit.FullName)  v$((Get-Item $hit.FullName).VersionInfo.FileVersion)"); break }
+    }
+}
+if (-not $pcdlrn) { W "  Pcdlrn.exe NOT found in standard dirs - PC-DMIS not installed where expected." }
+W ""
+
 W "================ UAC / registry virtualization ================"
 (reg query "HKLM\SOFTWARE\Microsoft\Windows\CurrentVersion\Policies\System" /v EnableLUA 2>&1 | Out-String) | W
 (reg query "HKLM\SOFTWARE\Microsoft\Windows\CurrentVersion\Policies\System" /v EnableVirtualization 2>&1 | Out-String) | W