When I try to update our XP client agents to 11.1a the update hangs at 95%

After a reboot the workstation agent can't communicate anymore with the servers.

I've got this error on 80% of our clients.

I've found this error in the system-update.log:

DEBUG;;;Found product info: PRODUCT_INFO:Novell ZENworks Endpoint Security Client:11.1.032
DEBUG;;;Attempting to resolve variable: content.0.path
DEBUG;;;variable not found in knownVariables or in environment : content.0.path
DEBUG;;;looking for item in content list
DEBUG;;;content id : 0af069c960bf81a01f8fa16de4668127
DEBUG;;;creating path: C:\Program Files\Novell\ZENworks\cache\zmd\ZenCache\1b892340-37f9-42c9-89f7-8f6baf978311\setup.exe
DEBUG;;;Attempting to resolve variable: content.0.path
DEBUG;;;variable not found in knownVariables or in environment : content.0.path
DEBUG;;;looking for item in content list
DEBUG;;;content id : 0af069c960bf81a01f8fa16de4668127
DEBUG;;;creating path: C:\Program Files\Novell\ZENworks\cache\zmd\ZenCache\1b892340-37f9-42c9-89f7-8f6baf978311\setup.exe
DEBUG;;;Attempting to resolve variable: ZENWORKS_HOME
DEBUG;;;Attempting to resolve variable: ZENWORKS_HOME
DEBUG;;;Attempting to resolve variable: ZENWORKS_LOGS
DEBUG;;;Attempting to resolve variable: UPDATE_GUID
DEBUG;;;launching: C:\Program Files\Novell\ZENworks\cache\zmd\ZenCache\1b892340-37f9-42c9-89f7-8f6baf978311\setup.exe
DEBUG;;;arguments: /s /v"/qn STRBR=ReallySuppress RESTARTZCM=0 INSTALLDIR=\"C:\Program Files\Novell\ZENworks\esm\" TARGETDIR=\"C:\Program Files\Novell\ZENworks\esm\" /lvx* \"C:\Program Files\Novell\ZENworks\logs\system-update\50110100001e69ca2ccb2865b42bf7b3\setup.exe. log\""
DEBUG;;;Unable to launch process C:\Program Files\Novell\ZENworks\cache\zmd\ZenCache\1b892340-37f9-42c9-89f7-8f6baf978311\setup.exe. C:\Program Files\Novell\ZENworks\cache\zmd\ZenCache\1b892340-37f9-42c9-89f7-8f6baf978311\setup.exe timed out
DEBUG;;;Attempting to resolve variable: content.0
DEBUG;;;variable not found in knownVariables or in environment : content.0
DEBUG;;;looking for item in content list
DEBUG;;;content id : 0af069c960bf81a01f8fa16de4668127
DEBUG;;;creating path: C:\Program Files\Novell\ZENworks\cache\zmd\ZenCache\1b892340-37f9-42c9-89f7-8f6baf978311\setup.exe
ERROR;MSI_INSTALL_ERROR;setup.exe,-1;