I saw your bump, and sorry for the delay.
I don't have any answers, just guesses and things to try.
1] "Your e-mail server rejected your login. Verify your username and password under account properties...."
This is nearly always incorrect account setup details. I can see that you say it works a subsequent time, but I would suggest you head over to your email provider's web page that explains how to setup email accounts and check through carefully the settings given.
2] When you transferred all Outlook files form XP to Vista, how did you transfer the Contact details? The best way is to "Export" from the old Contact list and then "Import" to the new one.
I'm guessing that because Vista's file locations are different to XP's, (for example, no longer any "Documents and Settings" folders), the path for Outlook's Contacts is different on Vista to that of XP.
So, if you still have the XP system, open Outlook and export the contacts list to a file, (if you have options which type of file, select CSV, comma separated values), then transfer that file to the new system and Import into Outlook.
I hope that helps.