Can't receive emails from new email account

I recently added a new email account to Outlook, replacing an old secondary
account with a new one. Had no trouble sending and receiving with the old
account, but with the new one, Outlook will send out emails, but won't
download them from the ISP server. The account settings are identical to the
old replaced account, and are the same as the unchanged primary account,
which continues to work fine. The problem doesn't appear to be at the ISP
end, as I can receive the downloaded emails fine with Outlook Express using
the same settings for the account as I am using with Outlook.

When I hit Send/Receive, the dialog box indicates that Outlook is performing
only one task and listing the primary account. With the old secondary
account, the dialog box would always indicate that it was performing two
tasks, and would list both accounts. When I test the account settings, all
tests are successful, but I can only retrieve the outgoing test email by
going to Outlook Express.

Any suggestions on where to go from here?