Citrix "Protocol Driver" error when launching an application

One of our Citrix Xenapp 5 servers wouldn't allow applications to be launched, giving a "protocol driver" error. After following the instructions on Citrix's web site (http://support.citrix.com/article/CTX108698) and rebooting the server, the server started working again.

Here are the steps I took, in short:

1. Disabled session reliability for the server in the Citrix Delivery Services Console
   
2. Deleted the ICA-tcp connection in Terminal Services Configuration on the effected server
   
3. Recreated the ICA-tcp connection
4. Re-enabled session reliability
5. Rebooted the server

I didn't have to recreate the LHC like the Citrix article says.