[Logician]

1- Creating a new user profile field is done inside Admin CP. I hope you first this method in the first place? It would be very unnecessary to use PhPmyadmin to add a new profile field.

If you created the field via Admin CP, I doubt it would give you this problem. It should not be server intensive to create a new user profile field even if your db is large.

2- Messing with db with PhpMyadmin is not recommended unless you know what you are doing. But if you are intended a new profile field has 2 traces in your db. Its name and options are recorded in "profilefield" table where one new column is also added to "userfield" table. Deleting its record from profilefield and deleting the column from userfield, should solve the problem IF IT IS RELATED to profile fields. (BACKUP DB!) But as I said before I doubt it, it might be another db problem you are having at the moment..