Our organizzation is running CiviCRM 4.6.8. We are setting up an event and participants can register online. while configuring the on-line registration page, we get the error:

Duplicate Matching Impossible The selected profiles do not contain the fields necessary to match registrations with existing contacts. This means all anonymous registrations will result in a new contact.

We have specified a custom profile to register participants. The profile includes as mandatory field, the ID number of the person as per their South African Identity document or passport. This field will allow us to uniquely identify each participant.

We have also created a custom dedupe rule (unsupervised) as follows: Field -> ID Number Length -> left this blank Weight -> 30 Weight Threshold to Consider Contacts 'Matching': 30

Why do we get this error and how can we resolve it? We need to ensure that a participant can register only once for this event, as it is a competition.

2 Answers 2


It seems your event registration profile form has no email field or last name field for duplicates checking, refer to this related post How to register for event without an email address?

Also refer to the following link for for more information on civi deduping: http://book.civicrm.org/user/common-workflows/deduping-and-merging/

  • Thanks for your response. My event registration profile definitely includes an email filed as well as a last name field. What I want to achieve is to use my user defined Dedupe rule that includes checking for match against the ID Number, First Name, Last Name and Email address. However, when I select this dedupe rule, i get the duplicate matching impossible error. If however, I select "Name and Email (reserved) - General", I don't get this error.
    – Sudesh
    Feb 6, 2016 at 20:26
  • Unsupervised rules are rules that are automatically checked when a user enters contact info into a form on the front end of the site (for example, when registering for an event, making a contribution) Is your dedupe rule set as unsupervised? Try editing the default unsupervised rule to add the additional fields : ID number ..
    – Kboy
    Feb 6, 2016 at 20:44
  • I have managed to get my rule to work - I found that it was not set to unsupervised. Thanks. I still have other problems with event registration email and PDF receipts not being sent if I set the PDF format to A4, Landscape. I guess, that is for another thread.
    – Sudesh
    Feb 7, 2016 at 12:54

CiviCRM 4.5 introduced the ability to select a special duplicate matching rule for your event. With this came the higher likelihood that the fields needed for matching aren't all included in the registration form. The Duplicate Matching Impossible error highlights that situation.

From your comments on Kboy's answer, it seems like you had picked a different matching rule than the one you set as Unsupervised, so that explains why you got the error.

However, you probably don't want such a specialized rule as your Unsupervised rule. The Unsupervised rule is used on online contributions and other front-end pages, so it should be a broadly-applicable one: perhaps email only, or email plus first name. It's unlikely that you'll ask ID numbers of your donors, so you've effectively made duplicate matching impossible on other forms. (There just isn't a warning to say so.)

To fix this, make a different rule Unsupervised (leaving your special rule as a General rule) and then go back to your event configuration form and select your special ID rule specifically.

A side note: I don't know how sensitive these South African ID numbers are, but you might consider what precautions should be taken when collecting and storing this information--and whether you should be asking for it in a form:

  • What are the consequences if an intruder (or even an unauthorized staff member) stole the numbers and corresponding names, addresses, etc.?
  • Are people commonly asked to provide their ID number online? Will participants be willing to do this?

I bring up these considerations because here in the U.S., everyone has a unique Social Security number, but it's sensitive enough that it's generally a bad idea to collect or store it in a CRM system.

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.