I have found that the K2 user module has prevented users from registering on my site. The user enters all their details, but is just returned to the login screen with nothing happening. I have disabled the K2 user plugin, and defaulted to the joomla login component and all is OK, except I have to add users to K2 groups manually.

Hello John,

Do you have template overrides for the k2 login module, profile.php or register.php of the component?
If so make sure if they are up to date. Download the latest version of K2 and check these files.

Regards

Thanks for your response. As I was looking for a solution, my hosting provider made some amendments to the server settings affecting emails, and now it seems to be working OK.