DotNetNuke (DNN) Error in Password Resetting

Error :

AssemblyVersion: 6.2.0

StackTrace:

Message: System.ArgumentNullException: Value cannot be null. Parameter name: input at System.Text.RegularExpressions.Regex.Replace(String input, String replacement) at DotNetNuke.Common.Utilities.HtmlUtils.StripWhiteSpace(String HTML, Boolean RetainSpace) at DotNetNuke.Services.Mail.Mail.SendMailInternal(MailMessage mailMessage, String subject, String body, MailPriority priority, MailFormat bodyFormat, Encoding bodyEncoding, IEnumerable`1 attachments, String smtpServer, String smtpAuthentication, String smtpUsername, String smtpPassword, Boolean smtpEnableSSL) at DotNetNuke.Services.Mail.Mail.SendEmail(String fromAddress, String senderAddress, String toAddress, String subject, String body) at DotNetNuke.Services.Mail.Mail.SendMail(UserInfo user, MessageType msgType, PortalSettings settings) at DotNetNuke.Modules.Admin.Users.ManageUsers.PasswordUpdated(Object sender, PasswordUpdatedEventArgs e) 

Solution : 

We tried out lot of things and finally finally figured out the error. It was that the subject localization key is missing in the GlobalResources.resx file. Once you add the following key 
EMAIL_USER_UPDATED_OWN_PASSWORD_SUBJECT.Text everything was working perfectly....