Try again and it may work fine the second time. If not, there is an article by Microsoft that will explain the problem. See details below.
According to Microsoft:
"This problem occurs on a Microsoft Windows 2000-based computer that has a third-party browser that does not support Dynamic Data Exchange (DDE), such as Netscape Navigator and Mozilla. "
1. Double-click My Computer.
2. On the View menu, click Folder Options.
3. On the File Types tab, click URL: MailTo Protocol in the Registered File Types list, and then click Edit.
4. In the Actions box, click Open and then click Edit.
5 Click to remove the Use DDE check box, and then click OK.
6. Click Close two times."