Customer Login problem

[#1]

Since yesterday when trying to login to the Member Centre I get the message shown below the first time I click the login button. Clicking the button for the second time, without changing anything else, gets me logged in successfully. Using FF4 and using saved passwords.
Not a big problem, but slightly annoying. Could this be linked to other connectivity problems?

[#2]

Have you tried deleting your cookies and temporary internet files?

[#3]

Thanks Adam.  On checking, I found I have been accumulating multiple Plusnet cookies - getting rid of them all and logging in again (first time), I now only have one, which seems reasonable.
Thanks to this checking I also found I had many cookies that I thought my regular use of CCleaner should have been been clearing, but was not! Now warned I will not be placing total reliance on that process any more.
edit: spoke too soon - problem back again this morning (Sunday) but I see other are experiencing similar problems so I will await developments
edit 2: re CCleaner - just downloaded latest version 3.07 and whereas the previous version 3.00 was showing no FF cookies to delete the latest version showed 33! - it also showed a much bigger Internet Cache to delete. This suggests to me that the earlier version was not compatible with the latest FF4 - is this worth flagging up elsewhere or did everyone else know this already.

[#4]

Thanks for replying Whiffler, glad you got that sorted. Windows cleaner can be a good alternative to CC. I prefer just deleting them myself via the browser menu, that way you can be sure that its done the trick.