Can't send emails in OE Express 6

I have been in an RV park in TX for the winter for the last 2 months and the free wi-fi has been great. Strong signal and fast. Email and internet working great. Using XP SP2 and FireFox.
3 days ago for no apparent reason I get errors when I try to send emails from any either my 2 accounts. I receive them fine. I checked the server settings and all appears well. I can take my laptop to the local Holiday Inn down the street and the same emails get sent just fine. In the park they have a cable modem and an unsecured network so anybody can use it free.
I also did a system restore to a time before the problem and ran the gamut of Virus scanner and spyware and adaware programs and nothing significant showed up.
Any ideas? Help.
Floyd

 

Thanks Steve, but according to the guy in charge of keeping the wi-fi running told me nothing has changed that he did.
Floyd