Solved - Cannot upgrade Xenapp 6.0 to Xenapp 6.5

I was super excited about the new Xenpp 6.5 with so many improvements focused on user experience and more. We have about 40 Xenpp 6.0 servers with over 500 users. So testing this was crucial as once you uninstall Xenapp 6.0 and install Xenapp 6.5, the only way of going back is restoring from the backup. I tried the upgrade utility provided by Citrix to no avail (http://support.citrix.com/article/CTX130614/). Xenapp 6.0 appeared to uninstall just fine but installation of Xenapp 6.5 failed. As many of you might already know there is no direct upgrade path from Xenpp 6.0 to Xenapp 6.5. The utility is merely a script that uninstalls all the components of Xenapp 6.0 and installs 6.5 and joins to the new Xenapp 6.5 farm. 

If i installed Xenapp 6.5 on a brand new server, it worked fine. But when i installed it on a server with Xenapp 6.0, using utility or manually uninstalling and installing it, it failed. After spending hours on research, i still couldnot make it work. There were many other people having the same problem, different solutions worked for different people. However, for me it was no luck. I finally managed to figured out that the problem was something to do with the Xenapp 6.0 not uninstalling properly, although all the components uninstalled successfully. 
Out of those 15 times i tried, this is how it worked for me

1. unjoin the Xenapp 6 server from the farm and uninstall Xenapp 6.0
2. Then uninstall all the citrix components.

 it might ask you to reboot after some of the uninstallations. I just rebooted it once after all the components were uninstalled. 
3. after the reboot, delete all the folders under C:\Program files (x86)\citrix\ except C:\Program files (x86)\citrix\Xentools (only if the VM is a Xen VM - you will have the Xen tools installed). You might get an access denied error for the folder C:\Program files (x86)\citrix\farmGPO. Take the ownership of the folder and then delete.
4. Next, open regedit, and delete all the keys under HKLM\software\citrix

5. reboot
6. Now install Xenapp 6.5 and the installation will succeed

Hope this helps :)

Citrix Xenapp 6.0 gives an error when users logon to the citrix web interface "An error occured when making the requested connection"

This error can occur because of a number of reasons concerning the Xenapp 6.0 server. Besides the obvious reason - the server does not have internet connectivity or is shut down, the tricky cause can be the load value for the server. This can be checked using the following command on the culprit Xenapp 6.0 server

QFARM /LOAD

This command will give you the list of the servers in the farm and their load value. If the load value of the server is 20000, it will refuse any further connections and give the above error. One more symptom is that you might not see the server in the list at all. This can be corrected by doing the following

1. Open Command prompt as administrator

2. Run the command "net stop imaservice" to stop the imaservice

3. Run the command "net start imaservice" to start the imaservice

NOTE: this can also be done through services.msc console but i have experienced that the imaservice tends to hang when restarted through services console. 

Once the service is restarted. The server will start accepting connections again.