Creating new users with Commerce & Rules: ERROR Commerce has a problem with the Rule to create a new User account for an anonymous order: 

ERROR: Missing configuration for parameter param_field_[fieldname]


According to a drupalcommerce.org comment this is because of fields being required: 


  The rule “Create a new account for an anonymous order” will fail if any of the fields it attempts to create are required. That failure will generate the ERROR: Missing configuration for parameter param_field_.


Despite this insight, no answer is give for how to take care of the error. It is necessary to my site to require some fields upon user registration. How can I get rid of this error?
During anonymous checkout, an email address is collected from the 'Account information' pane to create a new user (or append the order to an existing user).

You should be able to hook into the form on the 'Account information' pane and add your required fields. You will probably have to modify the rule (Create a new account for an anonymous order) to send along the extra fields for creating a new user with the required fields - when marked required, custom fields added to the user are added to the Create Entity action for user as well.

You can populate these fields using existing variables, or fields added to the Commerce Order or Commerce Billing Profile, or create your own variables (eg via hook_token_info_alter() to make variables available through the commerce_order).