Additional Information
Initially, when you are trying to modify the "Full Name" and/or "Email" fields under the Tools >> Preferences >> Custom Fields menu, VLM warns you with the following message.
All data associated with the selected fields will be deleted. NI VLM uses the information in the "Full Name" and "Email" fields to email clients. NI also uses this information to provide technical support and other benefits to your clients. Do you want to continue?

If you did this modification by mistake and deleted the associated data, you can follow the steps, described in the Restoring NI VLM from a Backup File article to restore the lost data.