We're dealing with a Windows Server 2008 R2 Terminal Server (version 6.1.7601) running in a VMware vSphere environment with:

• 4 vCPUs (no overcommitment)
• 32GB RAM allocation
• ~70 concurrent users (recent spike)

The system throws Event ID 1500 when new users attempt to logon during peak periods:

Windows cannot log you on because your profile cannot be loaded...
DETAIL - Insufficient system resources exist to complete the requested service.

Contrary to initial assumptions, this isn't primarily about RAM or CPU. The key constrained resources are:

• Session Paged Pool Memory (default 128MB limit)
• Desktop Heap allocation (default 3MB per session)
• GDI Object Handles (system-wide limit)

We can verify current usage with these PowerShell commands:

# Check session paged pool usage
Get-WmiObject -Class Win32_PerfRawData_PerfOS_System | 
Select-Object PoolPagedBytes

# Check desktop heap settings
reg query "HKLM\System\CurrentControlSet\Control\Session Manager\Memory Management" /v SessionPoolSize

These registry modifications can significantly increase capacity:

Windows Registry Editor Version 5.00

[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Session Manager\Memory Management]
"SessionPoolSize"=dword:00000040

[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Session Manager\SubSystems]
"Windows"=hex(2):25,53,79,73,74,65,6d,52,6f,6f,74,25,5c,73,79,73,74,65,6d,33,32,\
  5c,63,73,72,73,73,2e,65,78,65,20,4f,62,6a,65,63,74,44,69,72,3d,25,53,79,73,\
  74,65,6d,52,6f,6f,74,25,5c,73,79,73,74,65,6d,33,32,5c,43,53,52,53,53,20,53,\
  68,61,72,69,6e,67,53,65,63,74,69,6f,6e,3d,31,32,38,30,30,20,53,65,72,76,65,\
  72,44,6c,6c,3d,62,61,73,65,72,65,66,2c,31,2c,36,30,30,30,30,2c,36,30,30,30,\
  30,20,50,72,6f,66,69,6c,65,43,6f,6e,74,72,6f,6c,3d,4f,66,66,20,4d,61,78,52,\
  65,71,75,65,73,74,54,68,72,65,61,64,73,3d,31,36

Certain applications exacerbate the problem by:

• Creating excessive GDI objects (Excel, Visio)
• Loading large DLLs into each session (CAD software)
• Generating complex window hierarchies (legacy Win32 apps)

Use Process Explorer to identify offenders:

# GDI Objects per process
Get-Process | Sort-Object -Property GDIObjects -Descending | 
Select-Object Name, Id, GDIObjects -First 10

For monitoring thresholds, implement this PowerShell alert script:

$criticalThreshold = 90 # Percentage
$sessionPool = (Get-Counter "\Memory\Pool Paged Bytes").CounterSamples[0].CookedValue
$maxPool = (Get-ItemProperty "HKLM:\SYSTEM\CurrentControlSet\Control\Session Manager\Memory Management").SessionPoolSize * 1MB

if (($sessionPool / $maxPool * 100) -gt $criticalThreshold) {
    Send-MailMessage -To "admin@domain.com" -From "monitor@domain.com" 
        -Subject "Terminal Server Resource Alert" 
        -Body "Session paged pool usage exceeded $criticalThreshold%"
}

This error typically indicates exhaustion of non-paged pool memory in Windows kernel. Unlike regular RAM allocation, this special memory region handles:

- Network connections (SMB/NFS)
- Registry operations
- Security tokens
- Terminal Services session objects

Run these PowerShell commands during peak usage:

# Check non-paged pool usage
Get-Counter '\Memory\Pool Nonpaged Bytes' -Continuous

# Monitor session-specific resources
query session /server:localhost
qwinsta

Add these registry modifications (reboot required):

Windows Registry Editor Version 5.00

[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Session Manager\Memory Management]
"SessionPoolSize"=dword:00000004
"SessionViewSize"=dword:00000030

[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\LanmanServer\Parameters]
"Size"=dword:00000003

While Microsoft's theoretical limit is 16,384 sessions, real-world caps are:

- Light office apps: ~80-100 users
- Medium workloads: ~50-70 users
- Heavy CAD/design: ~30-50 users

Implement folder redirection via GPO:

<GroupPolicy xmlns="urn:schemas-microsoft-com:office:office">
  <FolderRedirection>
    <Properties action="Update" 
               path="\\fileserver\profiles\%USERNAME%"
               grantExclusive="no"/>
  </FolderRedirection>
</GroupPolicy>