It just means that someone bought your items on the ah and that your gold will be delivered soon.
The gold will be in new mail. It won't appear to that one. So you can just delete those empty "sale pending" mails.
I've used this macro to get rid of those empty mails, you might have to spam it a bit. 1 per mail.
Code:
/run if atbmi==nil then atbmi=1 end atbni=GetInboxNumItems() if atbmi>atbni then atbmi=1 end atbit=GetInboxInvoiceInfo(atbmi) if atbit=="seller_temp_invoice" then GetInboxText(atbmi); DeleteInboxItem(atbmi) else atbmi=atbmi+1 end