You're probably hitting database column size limits and won't be able to create anymore fields. Enable debug mode and maximum error reporting in Joomla global configuration then retry to expose the error.
Also, I need some integration between user profiles with contacts details in the Joomla contacts component. Is that possible?
We have no integration with Joomlas contact component. Joomla has its own system plugin that can create contact entries based off registrations though. The issue with this is Joomlas contact component is unique by name, but name is not unique so when you've 2 people registering with the same name you get a conflict and the user won't be able to register.