Joomla 2.5 frontend login not working but administrator on migration

this seems to be a common problem with a joomla 2.5 migration 


http://forum.joomla.org/viewtopic.php?t=714512


joomla frontend login not working after joomla 2.5 migration


joomla 2.5 frontend login not working after migration


joomla 2.5 changing mysqli to mysql broke my frontpage login




joomla 2.5 frontend login Your registration process is not yet complete message




Then it occured to me that I had Community Builder installed and this could be a link.  Which lead me to looking for this. 




joomla CB frontend login Your registration process is not yet complete message






This is as close to an answer that I got. 


http://www.joomlapolis.com/forum/154-advanced-members-support/195205-solved-cb-activation-email-not-working




In my case I'd realised I'd deleted some information about the user from the table 'comprofiler' - once reinstated I was up and working again.