using User Import module with date I was planning on using the user module to import more than 300 new users into my website. However, the birth date fields cannot be imported. Even before the actual import has started, I get these errors and warnings.

Warning: Creating default object from empty value in _user_import_settings_save() 
(line 574 of /sites/mywebsite.nl/dev/sites/all/modules/user_import/user_import.module).

Field Birthdate is not supported


Apparently the User Import module can't handle date fields. Can this be solved with the User Import module? Or is there another module that I can use to import my users? Or do I have to php this manually?

thanks in advance
You can use feeds module to import User. It can handle external fields also.
For more information go through the module documentation.