diff --git a/src/blackmisc/atomicfile.cpp b/src/blackmisc/atomicfile.cpp
index 4ab025cf9..b2c46f4e6 100644
--- a/src/blackmisc/atomicfile.cpp
+++ b/src/blackmisc/atomicfile.cpp
@@ -146,12 +146,9 @@ namespace BlackMisc
             : MoveFileEx(encode(fileName()).c_str(), encode(m_originalFilename).c_str(), MOVEFILE_WRITE_THROUGH);
         if (! result)
         {
-            m_renameError = true;
             wchar_t *s = nullptr;
             FormatMessage(FORMAT_MESSAGE_ALLOCATE_BUFFER | FORMAT_MESSAGE_FROM_SYSTEM, nullptr, GetLastError(), 0, reinterpret_cast<LPWSTR>(&s), 0, nullptr);
-            // MS 2018-09 Testing T321 ("failed to write session file")
-            //setErrorString((replace ? "ReplaceFile: " : "MoveFileEx: ") + QString::fromWCharArray(s).simplified());
-            CLogMessage(this).error((replace ? "ReplaceFile: " : "MoveFileEx: ") + QString::fromWCharArray(s).simplified() + "\n" + getStackTraceAlways().join("\n"));
+            const QString windowsError = (replace ? u"ReplaceFile: " : u"MoveFileEx: ") % QString::fromWCharArray(s).simplified();
             LocalFree(reinterpret_cast<HLOCAL>(s));
 
             // fall back to non-atomic remove-and-rename
@@ -160,11 +157,18 @@ namespace BlackMisc
                 QFile old(m_originalFilename);
                 if (!old.remove())
                 {
-                    setErrorString(old.errorString());
+                    // fall back failed, so report the reasons for the original failure AND the fall back failure
+                    m_renameError = true;
+                    setErrorString(windowsError % u" QFile::remove: " % old.errorString());
                     return;
                 }
             }
-            rename(m_originalFilename);
+            if (rename(m_originalFilename))
+            {
+                // fall back succeeded, so just log the reason for the original failure
+                CLogMessage(this).debug(u"CAtomicFile replacing %1: %2") << m_originalFilename << windowsError;
+            }
+            // else if rename() failed, then the reason is already reported by QFile
         }
     }
 #else
diff --git a/src/blackmisc/datacache.cpp b/src/blackmisc/datacache.cpp
index 34847537b..b98ce7732 100644
--- a/src/blackmisc/datacache.cpp
+++ b/src/blackmisc/datacache.cpp
@@ -491,7 +491,8 @@ namespace BlackMisc
 
         if (! revisionFile.checkedClose())
         {
-            CLogMessage(this).error(u"Failed to write to %1: %2 (%3 %4)") << revisionFile.fileName() << revisionFile.errorString() << QThread::currentThread()->objectName() << Q_FUNC_INFO;
+            static const QString advice = QStringLiteral("If this error persists, try restarting your computer or delete the file manually.");
+            CLogMessage(this).error(u"Failed to replace %1: %2 (%3)") << revisionFile.fileName() << revisionFile.errorString() << advice;
         }
     }
 
@@ -651,9 +652,17 @@ namespace BlackMisc
             timestamps.insert(key, timestamp);
             json.insert("timestamps", timestamps);
 
-            if (!(revisionFile.seek(0) && revisionFile.resize(0) && revisionFile.write(QJsonDocument(json).toJson()) && revisionFile.checkedClose()))
+            if (revisionFile.seek(0) && revisionFile.resize(0) && revisionFile.write(QJsonDocument(json).toJson()))
             {
-                CLogMessage(this).error(u"Failed to write to %1: %2 (%3 %4)") << revisionFile.fileName() << revisionFile.errorString() << QThread::currentThread()->objectName() << Q_FUNC_INFO;
+                if (!revisionFile.checkedClose())
+                {
+                    static const QString advice = QStringLiteral("If this error persists, try restarting your computer or delete the file manually.");
+                    CLogMessage(this).error(u"Failed to replace %1: %2 (%3)") << revisionFile.fileName() << revisionFile.errorString() << advice;
+                }
+            }
+            else
+            {
+                CLogMessage(this).error(u"Failed to write to %1: %2") << revisionFile.fileName() << revisionFile.errorString();
             }
         }
         m_lockFile.unlock();
@@ -804,9 +813,17 @@ namespace BlackMisc
         apps.replaceOrAdd(currentProcess);
         json.insert("apps", apps.toJson());
         json.insert("uuid", uuid.toString());
-        if (!(file.seek(0) && file.resize(0) && file.write(QJsonDocument(json).toJson()) && file.checkedClose()))
+        if (file.seek(0) && file.resize(0) && file.write(QJsonDocument(json).toJson()))
         {
-            CLogMessage(this).error(u"Failed to write to session file %1: %2 (%3 %4)") << m_filename << file.errorString() << QThread::currentThread()->objectName() << Q_FUNC_INFO;
+            if (!file.checkedClose())
+            {
+                static const QString advice = QStringLiteral("If this error persists, try restarting your computer or delete the file manually.");
+                CLogMessage(this).error(u"Failed to replace %1: %2 (%3)") << file.fileName() << file.errorString() << advice;
+            }
+        }
+        else
+        {
+            CLogMessage(this).error(u"Failed to write to %1: %2") << file.fileName() << file.errorString();
         }
     }