When launching applications from Web Interface to start a Secure Gateway session the error "Protocol Driver Error" is returned, and Event ID 103 appear in the Secure Gateway event log.

Event ID 103: "Incoming Citrix Gateway Protocol downstream data could not be processed"

Resolution 1:
The session reliability port 2598 may be blocked between the Secure Gateway and the Presentation Servers.

- Allow the port through the firewall/host packet filters.

Resolution 2:
The Citrix server's used for the Secure Ticket Authority may have been rebuilt. This will cause the ID of the STA to change which will break ticketing. To resolve the issue rerun the Secure Gateway Configuration Wizard and remove and re-add the STAs:

- Select Start | All Programs | Citrix | Administration Tools | Secure Gateway Configuration Wizard
- Click OK to accept product selection
- Click Next to accept configuration type
- Click Next to accept the certificate
- Click Next to accept inbound client connections
- Click Next to accept outbound connections
- Delete and re-add the existing STAs
- Click Next to accept the STA configuration
- Click Next to accept the Web Interface options
- Click Next to accept the logging level
- Click Finish to restart the Secure Gateway service

Resolution 3:
Connections to Citrix Secure Gateway 3.0 Fail With Version 9.200 of the ICA Client for 32-bit Windows - Protocol Driver Error
http://support.citrix.com/article/CTX110065

Install Hotfix SGE300W008
http://support.citrix.com/article/CTX114059