Windows 7

on WINDOWS 7 SEP is supported. [EDITED]
If you are running a fresh install of SEP
then follow this procedure
remove liveupdate and SEP
delete all the symantec folders and liveupdate folders
reboot the box
install SEP again and run liveupate.
Hope this helps

https://www-secure.symantec.com/connect/forums/windows-7-beta-and-sep-11-mr4

Down load virus definition from here and try to install..
The screen shot indicates virus definition is missing...
Is it a managed client or unmanaged client?(In your screen shot liveupdate button not grayed out this will be normally present in unmanaged clients or in managed client were the manual launch of liveupdate is allowed but by default is is disabled in managed clients)
 

If you are not using RU5 i will recoment you to use that since it is the only version of SEP which supported in Windows 7 by symantec officially 

Hi

Try this Link and Follow the Steps from Vista/Server 2008 step that is same for Windows 7

How to clear out corrupted definitions for a Symantec Endpoint Protection Client manually.
http://service1.symantec.com/support/ent-security.nsf/docid/2007123111551948

Make Sure the VirusDefs folder is Present under
C:\ProgramData\Symantec\Definitions\VirusDefs\

If there is no VirusDefs Folder Do Repair Installation of SEP

Then run Intelligent updater and then try to Run Liveupdate

Link for Intelligent Updater
http://service1.symantec.com/SUPPORT/ent-security.nsf/docid/2007100816530248

Note:Intelligent Updater will update only AV and AS

After running the intelligent Updater try to Run Liveupdate

Else Restart the Computer and Run Liveupdate

Stop the Symantec Endpoint Protection Services:
Click the Start button.
In the search bar type services and then press Enter.
Note: If the User Account Control prompt pops up click Continue.
Right-click Symantec Management Client and click Stop.
Right-click Symantec Endpoint Protection and click Stop.
Note: If you are unable to stop the Symantec Management Client you will need to temporarily disable Tamper Protection. Please see the Technical Information at the bottom of this document for instructions.
Delete the data from the Definition folders:
Virus Definitions
C:\ProgramData\Symantec\Definitions\VirusDefs\
- Delete all files and subfolders

WARNING: In the next steps you will edit the Windows registry. Back up the registry before you make any changes to it, because incorrect changes to the registry can result in permanent data loss or corrupted files. Modify only the registry values that are specified. For instructions, see How to back up the Windows registry.

Delete the data from the registry:
Click the Start button
Type regedit and press Enter
Navigate to:
HKEY_LOCAL_MACHINE\SOFTWARE\WOW6432Node\Symantec\SharedDefs
Delete the following values:
SRTSP
NAVCORP_70
DEFWATCH_10
SepCache3
SepCache2
SepCache1
Restart the Symantec Endpoint Protection Services:
Maximize the Services window.
Right-click Symantec Management Client and click Start.
Right-click Symantec Endpoint Protection and click Start.

Technical Information:
How to disable Tamper Protection:
Open and log into the Symantec Endpoint Protection Manager console
Click the Clients view.
Select the appropriate group.
Under the Policies tab, in the "Settings" section, click General Settings.
Under the Tamper Protection tab, uncheck Protect Symantec security software from being tampered with or shut down.
Click OK.

After doing this try to update using intelligent updater

How can the defintions can be corrupt when i am installing SEP for the first time on a brand new machine????????

It worked , I was able to install SEP 11.0.5 and now it has updated all the 3 components. My questions is now i am testing on one machine in few months we will have hundreds to client machines. What is the easy way to do this?