Recently, I encountered a puzzling issue where newly created Active Directory security groups wouldn't grant access to Windows shares, even when properly configured. Here's the exact situation:

1. Created AD security group "special data users"
2. Added my user account to the group
3. Configured share permissions to grant "Full Control" to this group
4. Attempted access → Permission Denied error
5. Workaround: Adding my user directly or using older groups worked

After extensive testing, I discovered several potential causes for this behavior:

• Group Policy Refresh Delay: AD changes might take 90+ minutes to propagate
• Kerberos Ticket Issues: Cached credentials might not reflect new group membership
• Share vs NTFS Permissions: The combination might be causing conflicts
• Token Filtering: Windows might be filtering the new group from your security token

Here's a PowerShell script to verify your group membership and permissions:

# Check effective group membership
whoami /groups | Select-String "special data users"

# Verify share permissions
Get-SmbShareAccess -Name "ShareName" | Format-Table -AutoSize

# Check NTFS permissions
(Get-Acl "C:\path\to\share").Access | Where-Object {
    $_.IdentityReference -like "*special data users*"
} | Format-Table -AutoSize

Windows has a hard limit on security token size (typically 64KB). If your user belongs to many groups, newer additions might get filtered out. Check with:

# Check token size warning events
Get-WinEvent -LogName Security -FilterXPath "*[System[EventID=4624]]" -MaxEvents 10 | 
Where-Object { $_.Message -like "*token*" }

When you need immediate access without waiting for AD replication:

# Method 1: Clear Kerberos tickets
klist purge

# Method 2: Force group policy update
gpupdate /force

# Method 3: Logoff and log back in
# (Sometimes the simplest solution works best)

If the issue persists, consider these architectural alternatives:

# 1. Use domain local groups instead of global groups
# 2. Implement access-based enumeration
Set-SmbShare -Name "ShareName" -FolderEnumerationMode AccessBased

# 3. Consider using claims-based authentication
#    (Requires Windows Server 2012 R2 or later)

Before concluding the troubleshooting process:

1. Verify AD replication status between domain controllers
2. Check event logs for security-related errors (Event ID 4625)
3. Test with a new test user account in the same group
4. Confirm the share is not set to "Allow access to Everyone" with Deny ACEs

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This is one of those Windows permission issues that can make you pull your hair out. You've created a shiny new Active Directory security group, assigned yourself to it, and granted this group Full Control permissions on a shared folder - yet you're still getting "Access Denied" errors. Meanwhile, older security groups or direct user permissions work just fine.

Let's methodically examine the potential causes:

1. Group Membership Replication Delay

When you add users to groups in Active Directory, the changes don't propagate instantly. Check replication status with:

repadmin /showrepl

Force replication if needed:

repadmin /syncall

2. Kerberos Token Issues

Windows uses Kerberos tickets that cache group memberships. Your existing session might not reflect new group memberships. Try:

klist purge
gpupdate /force

Then log off and back on.

3. Share vs NTFS Permission Conflicts

Remember Windows evaluates both share-level and NTFS permissions. Verify both:

# Check share permissions
net share [sharename]

# Check NTFS permissions
icacls [path_to_shared_folder]

4. AD Group Scope Problems

If your group is Domain Local but the share is on a member server, you might need to use Global or Universal groups instead. Check group scope with:

Get-ADGroup -Identity "special data users" | Select-Object GroupScope

When basic checks don't reveal the issue, dig deeper:

Security Log Analysis

Enable auditing and check Event Viewer logs:

# Enable auditing
auditpol /set /subcategory:"File Share" /success:enable /failure:enable

Effective Permissions Check

Use the built-in tool to verify what permissions you actually have:

# GUI method:
# Right-click folder → Properties → Security → Advanced → Effective Access

Here's a script to verify all aspects of the permission chain:

# Verify group membership
$user = $env:USERNAME
$groups = Get-ADUser $user -Properties memberof | Select-Object -ExpandProperty memberof
if ($groups -match "special data users") {
    Write-Host "User is in the security group"
}

# Verify share permissions
$share = Get-SmbShare -Name "ShareName" | Select-Object -ExpandProperty SecurityDescriptor
if ($share -match "special data users") {
    Write-Host "Group has share permissions"
}

# Verify NTFS permissions
$acl = Get-Acl -Path "C:\path\to\share"
$acl.Access | Where-Object {$_.IdentityReference -like "*special data users*"}

• Confirm the security group exists in the same domain as the share server
• Verify the group appears in your security token (use whoami /groups)
• Check for deny permissions that might override your access
• Ensure the share server can contact a domain controller