Run the iLok Manger to get the update...

And it refuses to install for me...

Come to think of it...2.5.2 wouldn't install either...

My iLok software gets broken.  I usually have to go to the site to get the latest version.

my iLok 2 ,just stop working today, uninstalled old one.

Downloaded the new one, same problem iLok do not work

I have unplugged the iLok, inserted it again reinstalled software, restarted the computer, and still this message
Any suggestion how to solve it ?

You might try going to Administrative Tools then click on Services then find your iLok manager in the list then right click and select properties and select "automatic- delayed start" from the drop down then hit apply. Mike Docy hipped me to that and I just tried it after updating. We'll see if it helps.

Yep, here are the details:
(cntr-alt-delete) then select "Task Manager".
Select the "Services" tab.
Find "PaceLicenseDservices", right-click and then select "Open Services".
A new window will open. Find "Pace License Services", right-click and select "Properties".
Go to tab "general" and find field "Startup Type"  and change to "Automatic (Delayed Start)"
Done.
 
Easier way to get to Services:
Computer management/Services and Applications/Services
 
Or as yorolpal said: Control Panel/Administrative Tools/Services

Thanks for posting about the update.  Trouble-free for me.  Installed fine, works like a charm.

Continued:
When you install the update it undoes the "delayed start" thing so you have to redo it after the update.
If it is still not running go to the  "Pace License Services" and if status is not "running"  select "start".
You may need to reboot a few times after that.

Soundblend
my iLok 2 ,just stop working today, uninstalled old one.

Downloaded the new one, same problem iLok do not work

I have unplugged the iLok, inserted it again reinstalled software, restarted the computer, and still this message
Any suggestion how to solve it ?

I've had this happen. I remove Pace and registry entries. Then it works.  After that I chant multiple times "Pace Sucks!"