I have purchased a license key for Ccleaner V6.03. But when I enter the same and try to activate, it says
You do see that occasionally if/when the licence server or system is busy or is undergoing checks/maintenance.
I know that there has been a glitch with the online 'Licence Lookup' service recently, so it may be maintenance related to fixing that.
As it says there: Try again in a couple of hours and if it's still not accessible by this evening please let us know.
In the meantime you can still use CCleaner in Free mode.
we have seen other people experience the same problem in recent months. in some of those cases, people found that their HOSTS file was blocking connections to the servers that were used for activating ccleaner-licenses.
my advice would be to try disabling your HOSTS file temporarily by renaming it to "nohosts."
normally, the HOSTS file is located at c:\windows\system32\drivers\etc."
are you using the "spybot s&d" program? if so, my guess is that that is the source of the problem.