Hi All, I FOUND THE PROBLEM (at least for me)
I have been trying for the past three days to fix my problem which was the front end login stopped working. No error message just refreshed page and ignoring every login and password even super admin.
I was running joomla 2.5.8 and followed the upgrade process as usual and upgraded to 2.5.9. I also upgrade my HikaShop to 2.1.0 then it all went horribly wrong, not being able to determine which upgrade was the culprit.
I trawled the forums looking for an answer and many people seemed to be experiencing similar problems with no real clear cut reason why (joomla has a history of login function stopping all the way back to 2008????? why is that?????)
So I decided to switch off every plugin (not the modules) and switch on, the ones that were turned off, one.... at.... a.... time.... and eventually I discovered that the login started working again after I had switched on the EUCookieDirectiveLite the plugin was switched off over a month ago (perhaps a good idea to delete unwanted plugins rather than keep them) and I still do not know why this plugin should effect joomla's login or if HikaShop's upgrade had anything to do with it.
I should also mention that I cleared all cookies from Chrome just before I noticed the login not working, not sure if that is relevant.
I hope this is of some help, I am still concerned about the fact that login problems have been around for so long!
Please add to this post if you find out why an switched off plugin should have an impact on logins after an upgrade, one for the hard core programmers.
Love & Unity
Bobfreedom