When a user accesses a published Citrix Desktop via web interface, there is a chance they launch two desktops even though the allowed limit is set to one. Due to the user double clicking the published desktop icon quickly they may bypass the limit whilst Citrix Xenapp catches up.
Cause:
Users rapidly clicking on published application icons can initiate multiple sessions prior to the application instance counter getting updated.
There are two articles from Citrix which resolve this issue. See links below:
http://support.citrix.com/article/CTX118656 (The registry fix here will only work with published apps.)
http://support.citrix.com/article/CTX124612
If you’re using Xenapp 6.5 and find that some of Xenapp servers are randomly kicking all users off and stop allowing logons. You also probably have hotfix XA650W2K8R2X64014 installed. See link below for a hotfix from Citrix which is supposed to resolve the issue.
http://support.citrix.com/article/CTX132912
This one seems to bug lots of Sophos AntiVirus admins.
When you install or try updating Sophos on a XP PC, the install tries installing but then fails. If you hover over the sophos icon located in the taskbar, it displays ‘update failed’.
The issue is highly likely to be related to permissions within the registry.
Try this:
The issue may be related to a permission issue on the following registry key:
HKLM\Software\Microsoft\WindowsNT\Current Version\Windows\
1) Locate the above key, if you get an error when clicking on the Windows key, you have located your problem. If you don’t chedck that everyone has not been denied rights to the key. If yes, continue with the procedure below.
2) Right click on the Windows registry key and click permissions you may find its empty. If it’s empty, click advanced and change the ownership to yourself.
3) Or You may find ‘Everyone’ with deny access, if this is the case click and remove the group ‘Everyone’ and click OK.
Right click the Windows key and if the permissions have been restored, the above key will show all of it’s permissions.
Try the install or update again
When new users login using Citrix Fundamentals 6, they receive the below error:
Error:
“Citrix XenApp license acquisition server from server: all licenses are currently in use. Please try again later”
But you know that all licenses are not in use.
You are right, the licenses are not in use. The Citrix licensing Manager is not telling the truth 
On your Citrix server:
1) Click Start
2) Click Programs
3) Click Citrix
4) Click Quick Start
5) Click Management
6) Click Licensing
7) A list of users will appear and you will find that all licenses are in use.
8.) Locate the uers who are not currently logged on and invoke the license
1) Locate the server.xml file at C:\Program Files\Citrix\Licensing\LS\conf
2) Take a copy just incase
3) Open server.xml in notepad
4) Locate password=(ENC… example below: (Password here is encrypted)
password=”(ENC-01)AdFz17cd2oNQ+LdddkjkzUyVf4ZhjboiJCuCiuiusbB5zk2P9iG” passwordExpired=”false” privileges=”admin”/>;
5) Remove the content between password=” ” and type a new password. As this is plain text, its not secure but will become encrypted further down.
6) Next change the PasswordExpired value from false to true
7) Save the changes
8.) Restart the licensing services. If this is not done, you will not be able to login
9) Login to Citrix license console
10) Login and you will be promoted to change your password. After you have changed your password it will become encrypted.
You find that your group policy for IE8 is applied successfully apart from the proxy settings.
I experienced a similar issue and eventually found the issue was due to group policy exceptions.
If any of your proxy exceptions start with http:// https:// www etc, the proxy part will not apply. But Group Policy results will show the policy has applied successfully.
Amend to servername or ip and try again. It should apply successfully. Seems to be an issue with Windows 2008, but works with other Operating Systems.
Or, if you are using a 32 bit version of Internet Explorer on a 64 bit version of Windows – try this link http://support.microsoft.com/kb/952031
If you are using Websense hosted for your web filtering and want to know whether your internet traffic is successfully reaching websense, logon to a machine
and type the below url in an internet browser. Handy tool from Websense. Thanks Websense 
http://query.webdefence.global.blackspider.com/?with=connection&with=policy
Locate the registry key for the mail store by browsing to the below location.
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\MSExchangeIS\<SERVER NAME>\Private-00000-0000-000e-0000-0000000000 (To locate the private guid for your mailstore click here)
If the value ‘Database Size Limit in GB’ already exists, change the value to the new size in GB.
If the value does not exist within the registry, add the DWORD value ‘Database Size Limit in GB’ and set the value as required. Select decimal before setting the value.
For the change to affect straight away, you must restart the information store service. An event id of 1216 will be logged within the event log to confirm the change has been made.
If you can not restart the information store service at this time, you can wait until the automated Exchange online defrag takes place over night.
1) Launch Exchange command shell
2) Type the below command, amending, database name, server name etc as required and press enter.
Get-MailboxDatabase -Identity “<server name>\<storage group name>\<database name>” | Format-Table Name, GUID
3) If you experience issues with the above command such as error domain controller not found, another way to locate the guid is by typing the below command. This will list all mailstores along with the guid.
Get-MailboxDatabase | Format-List
Your group policy which sets the homepage stops working all of a sudden.
Experienced the same issue so downloaded the IE7 adm from the Microsoft website and loaded a new copy to the c:\windows\inf folder on the domain controller.
Tried again and the homepage loaded straightaway.
So issue was related to a corrupted IE7 adm file.
