Recent upgrade to VM system has caused User registration to break

[ryangrnr]

Currently we are using Joomla 2.5.22 and PHP 5.4.29. Recently we upgraded our VM system from 2.0.8c to 2.6.6. However by doing this it appears that when trying to create an account through VM you always get the error 'Username and password do not match or you do not have an account yet.'
I've tried multiple fixes, one of which was disabling the KC VM Registration Redirect plugin we are currently so that people could create accounts through Joomlas default registration form. With this you could create an account, and the shopper showed up in the virtuemart system, albeit with only the most basic information. However when you try to then edit the details through the account details page, you get logged out and returned to the front page with no error message and without the data being saved.
Another solution I tried was renewing the virtuemart config from file, but that did not help either.
I've also tried updating the tables through virtuemart tools.
Currently SEF is enabled on the site configuration, and there were no problems with the user creation before this update.
Here is a link to the user creation page: http://messerschmitt.co.uk/schmittparts.com/index.php/account-details
Can anyone help with this? I'm rather stumped on what could possibly be causing it.
Thanks

[slammy]

I am not sure but it sounds similar to a situation I was facing some time ago. See this thread (end of it): http://forum.virtuemart.net/index.php?topic=123064.msg421412#msg421412
I think the problem was caused by an package-installation-error at the end, while the process tried to write into a folder without having the rights for it (provider-logs Folder). That caused a non-finished/uncompleted Installation and I think there is some important SQL at the end of the Installation-process. Besides, between thosse versions (joomla) they did changed the crypt-method for Passwords!).   
Did errors occured while the Installation?

regards jens

[ryangrnr]

So do you think a Joomla update could also be part of the problem? As far as I remember I do not remember any update errors for either virtuemart or joomla 
Do you suggest I revert to a previous version of Joomla and see if that works? I'm not so sure that its an error to do with password authentication as it only happens on the VM side and not the joomla side for users, and people with accounts can still log in.
Thanks

[slammy]

Aah ok - no errros during Installation. I would suggest to you that you install joomla 2.5.17 and see if the registration does work again, like it was in my case The change of the cryptographic algorithm (from mcrypt to bcrpyt) by joomla started with version 2.5.18, so 2.5.17 is a good idea to test again.

Did you used file-Installation or the all-in-one installer to update vm? If you installed the packages from dev.virtuemart.net, give the allinone installer a try, but go back before to jml 2.5.17 and your used vm-version. then do the all-in-one.
regards jens

[ryangrnr]

Thanks for your suggestion jens, alas reverting joomla to 2.517 and upgrading didnt work. I've decided to restore my backup and try and get the upgrades working on a test site, thanks for your help!