Most of the time when there's a problem with a web-based application, such a Microsoft Outlook Web Access, it's got something to do with the browser.
We internet users love to load software, and software companies love to have their products integrate with web browsers via plugins. If the browser you're using has extra toolbars or a bunch of various buttons along the top that you're not familiar with, it's possible there could be a conflict with one of the plugins or a pop-up blocker.
Another problem could be the security settings within the browser. Default browser settings should allow the sending of email, and do not include the loading of add-ons.
Communicate with the owner and ask if it's okay for you to try to reset the browser to default settings. Make sure he or she understands that toolbars, buttons, or cached information, such as remembered password on websites, will be lost. If that's OK, go into the browser's options and look for a "reset to defaults" option.
For information on troubleshooting and resetting Internet Explorer 8, read this article: http://www.brighthub.com/computing/windows-platform/articles/44681.aspx
If resetting the browser doesn't work, ask if you could install a different browser such as Firefox or Google Chrome.