diff --git a/lam/HISTORY b/lam/HISTORY
index c7c079646..f64845d5e 100644
--- a/lam/HISTORY
+++ b/lam/HISTORY
@@ -1,4 +1,5 @@
 December 2025 9.4
+ - Main configuration and server profiles require latest file format (introduced in 9.0) (389)
  - LAM Pro:
   -> SMS sending can be done with email2SMS providers (465)
 
diff --git a/lam/docs/manual-sources/chapter-installation.xml b/lam/docs/manual-sources/chapter-installation.xml
index 8f7c65c64..9c761534e 100644
--- a/lam/docs/manual-sources/chapter-installation.xml
+++ b/lam/docs/manual-sources/chapter-installation.xml
@@ -608,6 +608,18 @@
       version. Unless explicitly noticed there is no need to install an
       intermediate release.</para>
 
+      <section>
+        <title>9.3 -&gt; 9.4</title>
+
+        <para><emphasis role="bold">New configuration format for main
+        configuration and server profiles is enforced.</emphasis> Please save your main
+        configuration and all server profiles with LAM 9.0 - 9.3 before
+        upgrading. You can also export your configuration and import all
+        server profiles and main configuration. This format change does not
+        apply if you use MySQL for configuration
+        storage.</para>
+      </section>
+
       <section>
         <title>9.2 -&gt; 9.3</title>
 
diff --git a/lam/lib/config.inc b/lam/lib/config.inc
index 3b1feae1e..1edd7a6f0 100644
--- a/lam/lib/config.inc
+++ b/lam/lib/config.inc
@@ -570,66 +570,19 @@ class ServerProfilePersistenceStrategyFiles implements ServerProfilePersistenceS
 		$config = new LAMConfig();
 		$confFilePath = $this->getPath($name);
 		if (!is_file($confFilePath)) {
+			logNewMessage(LOG_ERR, 'No such file ' . $confFilePath);
 			throw new LAMException(_('Unable to read file.'));
 		}
 		$file = @fopen($confFilePath, "r");
 		if (!$file) {
+			logNewMessage(LOG_ERR, 'Unable to open for reading: ' . $confFilePath);
 			throw new LAMException(_('Unable to read file.'));
 		}
 		$json = fread($file, 1000000);
 		$data = json_decode($json, true);
 		if ($data === null) {
-			fclose($file);
-			$file = @fopen($confFilePath, "r");
-			$data = [];
-			$moduleSettings = [];
-			$typeSettings = [];
-			$toolSettings = [];
-			$jobSettings = [];
-			while (!feof($file)) {
-				$line = fgets($file, 1000000);
-				$line = trim($line);  // remove spaces at the beginning and end
-				if (($line === "") || ($line[0] === "#")) {
-					continue; // ignore comments and empty lines
-				}
-				// search keywords
-				$parts = explode(': ', $line);
-				$keyword = $parts[0];
-				$keyword = trim($keyword, ':');
-				$startIndex = strlen($keyword) + 2;
-				$value = (count($parts) > 1) ? substr($line, $startIndex) : '';
-				if (!in_array($keyword, ['modules', 'types', 'tools', 'jobs'])) {
-					$data[$keyword] = $value;
-				}
-				else {
-					$subKeyword = $parts[1];
-					$startIndex = $startIndex + strlen($subKeyword) + 2;
-					$option = substr($line, $startIndex);
-					if (empty($option)) {
-						continue;
-					}
-					// module settings
-					if ($keyword === 'modules') {
-						$moduleSettings[$subKeyword] = explode(LAMConfig::LINE_SEPARATOR, $option);
-					}
-					// type settings
-					if ($keyword === 'types') {
-						$typeSettings[$subKeyword] = $option;
-					}
-					// tool settings
-					if ($keyword === 'tools') {
-						$toolSettings[$subKeyword] = $option;
-					}
-					// job settings
-					if ($keyword === 'jobs') {
-						$jobSettings[$subKeyword] = explode(LAMConfig::LINE_SEPARATOR, $option);
-					}
-				}
-			}
-			$data['moduleSettings'] = $moduleSettings;
-			$data['typeSettings'] = $typeSettings;
-			$data['toolSettings'] = $toolSettings;
-			$data['jobSettings'] = $jobSettings;
+			logNewMessage(LOG_ERR, 'Unable to read JSON from ' . $confFilePath);
+			throw new LAMException(_('Unable to read file.'));
 		}
 		fclose($file);
 		$config->importData($data);
@@ -3211,25 +3164,7 @@ class LAMCfgMain {
 				$this->importData($data);
 			}
 			else {
-				// fallback to old format
-				fclose($file);
-				$file = @fopen($this->conffile, "r");
-				while (!feof($file)) {
-					$line = fgets($file, 1000000);
-					$line = trim($line);  // remove spaces at the beginning and end
-					if (($line === "") || ($line[0] === "#")) {
-						continue; // ignore comments
-					}
-					// search keywords
-					for ($i = 0; $i < count($this->settings); $i++) {
-						$keyword = $this->settings[$i];
-						$keylen = strlen($keyword);
-						if (strtolower(substr($line, 0, $keylen + 2)) === strtolower($keyword . ": ")) {
-							$this->$keyword = substr($line, $keylen + 2, strlen($line) - $keylen - 2);
-							break;
-						}
-					}
-				}
+				throw new LAMException(_('The config file is not readable.'));
 			}
 			fclose($file);
 		}
diff --git a/lam/templates/login.php b/lam/templates/login.php
index 304ed3347..0a0afc07c 100644
--- a/lam/templates/login.php
+++ b/lam/templates/login.php
@@ -215,7 +215,7 @@ setlanguage(); // setting correct language
  * @throws LAMException error rendering login page
  */
 function display_LoginPage(?LAMLicenseValidator $licenseValidator, ?string $error_message, ?string $errorDetails = null, ?string $extraMessage = null): void {
-	$config_object = $_SESSION['config'];
+	$config_object = $_SESSION['config'] ?? null;
 	$cfgMain = $_SESSION["cfgMain"];
     if (!($cfgMain instanceof LAMCfgMain)) {
         die();
@@ -263,6 +263,9 @@ function display_LoginPage(?LAMLicenseValidator $licenseValidator, ?string $erro
 			echo "<br>";
 		}
 	}
+    elseif ($error_message !== null) {
+        StatusMessage("ERROR", $error_message);
+    }
 	else {
 		StatusMessage('WARN', _('Please enter the configuration and create a server profile.'));
 	}
diff --git a/lam/tests/utils/configuration.inc b/lam/tests/utils/configuration.inc
index d980ccef4..ab189b60d 100644
--- a/lam/tests/utils/configuration.inc
+++ b/lam/tests/utils/configuration.inc
@@ -36,6 +36,9 @@ function testCreateDefaultConfig() {
 		unlink($cfgPath);
 	}
 	touch($cfgPath);
+	$fileHandle = fopen($cfgPath, 'w');
+	fwrite($fileHandle, '{}');
+	fclose($fileHandle);
 	$serverProfilePersistenceManager = new ServerProfilePersistenceManager();
 	$config = $serverProfilePersistenceManager->loadProfile(LAMConfigTest::FILE_NAME);
 	$_SESSION['config'] = $config;