Today i faced a very complex problem. My Clients were complaining that they are are getting Citrix Protocol Driver Error. After initial troubleshooting i found that there were some http errors on my web interface servers. I restarted IIS on WIS but no luck. I restarted IMA service on Presentations servers but issue still remained same. It was strange that i am getting this error for all Applications published on different servers this means that this error is not server dependent. i have tried Citrix article http://support.citrix.com/article/CTX106531 published on same issue and also tried disabling Session reliability http://support.citrix.com/article/CTX108439 but no luck. My Citrix environment consists of 2 Access gateway servers, 2 Web interface servers, 4 presentation servers and 1 license servers and we are using Netscaler device for load balancing. For narrowing issue i have disabled one web interface server from Load balancer and configured application to use only one presentation server but it didn’t solved the problem. I also restarted whole farm but no luck. Then i focused on Access gateway appliance and removed 1 appliance from Load balancing but issue remained same after that i enabled 1st device in Load balancing and removed second device from load balancing then after test i found that the issue is not occurring again and it is solved. I then logged on to the the troubled access gateway and found that this sever is not able to connect to the license server also this server is not configured to accept connections on port 80 only https. i am not sure why the sessions are not going to the other Access gateway which have correct configuration. I have to still fixed the licensing server connection issue but till now i haven't got any complain from the user.