Unable to email invoices

this message came to me from a client- does anyone have this issue please?
Whatever site you are using to host the invoice has an invalid security certificate. Is it possible for you to just attach it and email it to me?

If you want to email raw PDF make sure Send as online PDF option is unchecked when emailing.

Hi, could some one perhaps help me with a issue im having when emailing a sales quote, it keeps on telling me The underlying connection was closed: An unexpected error occurred on a send. Yet my email is working just fine.
Thank You

Could it be that i have windows XP?