I don't use Outlook much, but a good first step might be to try an online virus scan [HouseCall is pretty good:
http://housecall.trendmicro.com ] and perhaps also update the definitions for whatever antivirus your friend already has installed, and do a full system "thorough" antivirus scan in Safe Mode. While in Safe Mode, run an antispyware program [if there's none on the computer, AdAware's a good start
http://www.lavasoft.de - and SpyBot is recommended as well
http://www.safer-networking.org ]
If it's not due to a malware infection, perhaps a repair-reinstall of Outlook might work.
Other techs more familiar with Outlook might have seen this one before, and have an easier solution - so keep checking back.
. . . Gary