I'm trying to test the SMTP setup via the test link on the Host Settings page.

Two days ago this worked, now I get an error:

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DotNetNuke.Services.Exceptions.ModuleLoadException: Value cannot be null. Parameter name: input ---> System.ArgumentNullException: Value cannot be null. Parameter name: input at System.Text.RegularExpressions.Regex.Replace(String input, String replacement) at System.Text.RegularExpressions.Regex.Replace(String input, String pattern, String replacement) at DotNetNuke.Common.Utilities.HtmlUtils.StripWhiteSpace(String HTML, Boolean RetainSpace) at DotNetNuke.Services.Mail.Mail.SendMail(String MailFrom, String MailTo, String Cc, String Bcc, MailPriority Priority, String Subject, MailFormat BodyFormat, Encoding BodyEncoding, String Body, String Attachment, String SMTPServer, String SMTPAuthentication, String SMTPUsername, String SMTPPassword) at DotNetNuke.Services.Mail.Mail.SendMail(String MailFrom, String MailTo, String Bcc, String Subject, String Body, String Attachment, String BodyType, String SMTPServer, String SMTPAuthentication, String SMTPUsername, String SMTPPassword) at DotNetNuke.Modules.Admin.Host.HostSettingsModule.cmdEmail_Click(Object sender, EventArgs e) --- End of inner exception stack trace ---
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Any ideas what might be the cause? I have not made any changes to the the setup and the sys admin claims the mail server is working correctly.

The problem actually occurs whenever I send mail from any of the mail forms within the site.

TIA

John