diff --git a/tech_docs/lab/AD_planning.md b/tech_docs/lab/AD_planning.md
index a93677e..9263601 100644
--- a/tech_docs/lab/AD_planning.md
+++ b/tech_docs/lab/AD_planning.md
@@ -208,3 +208,58 @@ graph TD
 
 Would you like a **version with links or tooltips** for web display (e.g., GitHub Pages or MkDocs)? Or a printable PNG/SVG export for slide decks or internal wikis?
 
+Ah, good catch! That error is due to special characters or formatting that Mermaid doesn’t handle well **inside square brackets**. Specifically, the parentheses in `Group Policy Objects (GPOs)` are not valid in label definitions inside `[]`.
+
+Here’s the **corrected version** of the diagram with compliant syntax:
+
+---
+
+### ✅ Fixed Mermaid Diagram – Active Directory Deployment Planning
+
+```mermaid
+graph TD
+  A[corp.example.com] --> B[Organizational Units]
+  A --> C[Sites and Services]
+  A --> D[Naming Conventions]
+  A --> E[Group Policy Objects]
+
+  B --> B1[Employees]
+  B1 --> B1a[HR]
+  B1 --> B1b[Engineering]
+  B1 --> B1c[Sales]
+  B --> B2[Service Accounts]
+  B --> B3[Workstations]
+  B3 --> B3a[Laptops]
+  B3 --> B3b[Desktops]
+  B --> B4[Servers]
+  B4 --> B4a[App Servers]
+  B4 --> B4b[File Servers]
+
+  C --> C1[Site NY - 192.168.10.0/24]
+  C --> C2[Site LA - 192.168.20.0/24]
+  C1 --> C3[Domain Controller NY]
+  C2 --> C4[Domain Controller LA]
+  C --> C5[Site Link NY-LA]
+
+  D --> D1[Usernames: firstname.lastname]
+  D --> D2[Computers: location-dept-serial]
+  D --> D3[Groups: purpose-scope-region-desc]
+
+  E --> E1[Security Policies]
+  E --> E2[Desktop Settings]
+  E --> E3[Software Deployment]
+
+  E1 --> E1a[Password Policy]
+  E1 --> E1b[Account Lockout Policy]
+
+  E2 --> E2a[Wallpaper Settings]
+  E2 --> E2b[Control Panel Restrictions]
+
+  E3 --> E3a[Office Deployment]
+```
+
+---
+
+This version will render without errors in Mermaid.js parsers (like in Markdown viewers or tools like Obsidian, MkDocs, VS Code extensions, etc.).
+
+Would you like me to also generate a **dark-mode variant**, or an **SVG version** you can embed into a GitHub repo or documentation?