On MetaFrame Presentation Server 3.0 (Windows Server 2003), MetaFrame XP 1.0 (Windows Server 2000), Presentation Server 4.0 (Windows Server 2003) or Presentation Server 4.5 (Windows Server 2003) you could find the following error message in your Systemlog:

Citrix Presentation Server 4.0 - Eventlog Error 9006, Source MetaFrame

Auto Client Reconnect attempted but failed due to incorrect cookie data.
NOTE: If this error occurs frequently it may indicate an attempt to gain
unauthorized access to the system.

You may receive this error, if a client takes too long to reconnect. On a Citrix-Server, you can type in the following command to raise the timeout for this particular server:

acrcfg /inherit:off && acrcfg /duration:900000

The first command disables the inheritance of the farmwide settings. The second one raises the timout limit ti 900.000ms, which are 15 minutes. Or, on a Citrix-Server, you could change the default timeout for the whole farm utilizing this command:

acrcfg /farm /duration:900000

Citrix Presentation Server 4.0 - acrcfg.exe

The tool is located in your Citrix installation folder I:\Program Files\Citrix\System32, whereas “I:” represents the drive on which Citrix is installed.