TWAIN option disappears after scanning to email in Acrobat 6 & 8

We have a user who was running Acrobat 6 and a Fujitzu scanner on Windows XP who prefers the scanner's TWAIN driver.  Whenever a scan is sent from Acrobat via email, the TWAIN driver is no longer accessible within the application and the user must fully exit Acrobat before they are able to use the TWAIN scanner again.  We have upgraded her to Acrobat 8, but the problem persists.  No errors are received, but after the email is sent, the TWAIN driver is no longer an option for the user until Acrobat is closed and then reopened.