diff --git a/webui/web/dashboard.html b/webui/web/dashboard.html
index fd13bf6e..52efb32a 100644
--- a/webui/web/dashboard.html
+++ b/webui/web/dashboard.html
@@ -419,10 +419,19 @@ under the License.
     }
 
     async function loadGatewayUsers() {
+      if (!api.canManageGatewayUsers()) return true;
+
       let users;
       try {
         users = await api.listUsers();
       } catch (error) {
+        if (error.code === 'XAdminMethodNotSupported') {
+          api.setCanManageGatewayUsers(false);
+          document.querySelectorAll('[data-admin-users-only]').forEach(item => {
+            item.style.display = 'none';
+          });
+          return true;
+        }
         console.error('Error loading users:', error);
         showToast('Error loading users: ' + error.message, 'error');
         return false;
diff --git a/webui/web/js/api.js b/webui/web/js/api.js
index 6c690ac6..ce8a6075 100644
--- a/webui/web/js/api.js
+++ b/webui/web/js/api.js
@@ -124,6 +124,7 @@ class VersityAPI {
     this._hasIAM = false;       // Credentials validate against the IAM service
     this._hasS3 = false;        // Credentials validate against the S3 data plane
     this._canListBuckets = false; // hasS3 is true and s3:ListAllMyBuckets is allowed
+    this._canManageGatewayUsers = true; // False when the gateway runs in single-user mode
   }
 
   /**
@@ -295,6 +296,21 @@ class VersityAPI {
     sessionStorage.setItem('vgw_can_list_buckets', this._canListBuckets ? 'true' : 'false');
   }
 
+  /**
+   * Check whether this gateway supports its account-management Admin API.
+   */
+  canManageGatewayUsers() {
+    return this._canManageGatewayUsers;
+  }
+
+  /**
+   * Record whether the gateway supports its account-management Admin API.
+   */
+  setCanManageGatewayUsers(canManageGatewayUsers) {
+    this._canManageGatewayUsers = !!canManageGatewayUsers;
+    sessionStorage.setItem('vgw_can_manage_gateway_users', this._canManageGatewayUsers ? 'true' : 'false');
+  }
+
   /**
    * Load credentials from sessionStorage
    */
@@ -310,6 +326,7 @@ class VersityAPI {
     const hasIAM = sessionStorage.getItem('vgw_has_iam') === 'true';
     const hasS3 = sessionStorage.getItem('vgw_has_s3') === 'true';
     const canListBuckets = sessionStorage.getItem('vgw_can_list_buckets') === 'true';
+    const canManageGatewayUsers = sessionStorage.getItem('vgw_can_manage_gateway_users') !== 'false';
 
     // Support legacy single endpoint storage
     const legacyEndpoint = sessionStorage.getItem('vgw_endpoint');
@@ -325,6 +342,7 @@ class VersityAPI {
       this._hasIAM = hasIAM;
       this._hasS3 = hasS3;
       this._canListBuckets = canListBuckets;
+      this._canManageGatewayUsers = canManageGatewayUsers;
       return true;
     }
     return false;
@@ -343,6 +361,7 @@ class VersityAPI {
     this._hasIAM = false;
     this._hasS3 = false;
     this._canListBuckets = false;
+    this._canManageGatewayUsers = true;
     this._userType = 'user';
     this._accessibleGateways = [];
     sessionStorage.removeItem('vgw_admin_endpoint');
@@ -357,6 +376,7 @@ class VersityAPI {
     sessionStorage.removeItem('vgw_has_iam');
     sessionStorage.removeItem('vgw_has_s3');
     sessionStorage.removeItem('vgw_can_list_buckets');
+    sessionStorage.removeItem('vgw_can_manage_gateway_users');
     sessionStorage.removeItem('vgw_iam_probe_error');
     sessionStorage.removeItem('vgw_user_type');
     sessionStorage.removeItem('vgw_accessible_gateways');
@@ -857,7 +877,9 @@ class VersityAPI {
     const responseText = await response.text();
 
     if (!response.ok) {
-      throw new Error(parseXmlErrorMessage(responseText, `HTTP ${response.status}: ${response.statusText}`));
+      const error = new Error(parseXmlErrorMessage(responseText, `HTTP ${response.status}: ${response.statusText}`));
+      error.code = parseXmlErrorCode(responseText);
+      throw error;
     }
 
     return responseText;
@@ -2851,6 +2873,18 @@ function parseXmlErrorMessage(responseText, fallback) {
   return fallback;
 }
 
+/**
+ * Extract an S3-compatible error code from an XML response body.
+ */
+function parseXmlErrorCode(responseText) {
+  try {
+    const xmlDoc = new DOMParser().parseFromString(responseText, 'text/xml');
+    return xmlDoc.querySelector('Code')?.textContent || null;
+  } catch (e) {
+    return null;
+  }
+}
+
 /**
  * Normalize a parsed member-list field to an array
  */
diff --git a/webui/web/js/app.js b/webui/web/js/app.js
index a57c13c1..04c42d91 100644
--- a/webui/web/js/app.js
+++ b/webui/web/js/app.js
@@ -101,6 +101,10 @@ function requireGatewayUsers() {
     window.location.href = 'iam-users.html';
     return false;
   }
+  if (!api.canManageGatewayUsers()) {
+    window.location.href = defaultLandingPage();
+    return false;
+  }
   return requireAdmin();
 }
 
@@ -420,9 +424,9 @@ function updateUserInfo() {
  *                         standalone-IAM deployment
  *   data-s3-only          the S3 data plane answered for these credentials
  *   data-iam-only         the standalone IAM service answered for them
- *   data-admin-users-only the inverse of data-iam-only: the gateway's own
- *                         account store is still the user directory, rather
- *                         than a configured standalone IAM service
+ *   data-admin-users-only the gateway's own account store is available for
+ *                         management, rather than standalone IAM or
+ *                         single-user mode
  */
 function initSidebarWithRole() {
   initSidebar();
@@ -435,7 +439,7 @@ function initSidebarWithRole() {
   if (!api.hasManagement()) hide('[data-management-only]');
   if (!api.hasS3()) hide('[data-s3-only]');
   if (!api.hasIAM()) hide('[data-iam-only]');
-  if (api.hasIAM()) hide('[data-admin-users-only]');
+  if (api.hasIAM() || !api.canManageGatewayUsers()) hide('[data-admin-users-only]');
 
   reportIAMProbeFailure();
 }