GrabCAD Print White Screen on Startup

1. Problem Description

Upon launching GrabCAD Print, the application hangs on a pure white screen. Reboots and reinstalls do not resolve the issue.

2. Root Cause

The issue is caused by a TCP Port Exclusion. GrabCAD Print relies on internal "API Services" (PolyJet, Origin, and RPS) that communicate over local ports 6552 and 6553.

Windows (specifically via Hyper-V or WSL2) occasionally reserves large blocks of "excluded" ports for system use. If the range includes 6552–6553, the GrabCAD background services fail to start with an Access Denied or ECONNREFUSED error. Since the UI cannot communicate with its engine, it remains blank.

3. Verification Steps

To confirm this is the issue, run the following in PowerShell (Admin):

netsh interface ipv4 show excludedportrange protocol=tcp

If the range 6552–6553 falls within any "Start Port" and "End Port" listed, the ports are blocked by the OS.

4. Resolution Procedure

Phase A: Releasing the Blocked Ports

1. Close GrabCAD Print and all related processes in Task Manager.
2. Open PowerShell as Administrator.
3. Stop the Network Address Translation (WinNAT) service to release the dynamic port reservations:

   net stop winnat
   

4. Launch GrabCAD Print. The application should now start successfully as the ports are no longer restricted.

Phase B: Permanent Prevention (Persistent Reservation)

To prevent Windows from "stealing" these ports again after a future reboot, you must manually reserve them for GrabCAD:

1. While the winnat service is still stopped, run:

   netsh int ipv4 add excludedportrange protocol=tcp startport=6552 numberofports=2 store=persistent
   

2. Restart the network service:

   net start winnat
   

5. Summary Table for IT/Helpdesk