Does bad luck indeed come in threes? A Microsoft security fix for Outlook Express could be the third of last week's patches to cause trouble for some users.

Microsoft has received some reports of trouble with the update, a company representative said on Thursday. Microsoft had already acknowledged that two of the other five updates it released on "Patch Tuesday" last week can, in some cases, cause problems for users.

Microsoft is still investigating the issues related to the Outlook Express patch. "Nothing is confirmed yet," the representative said in an e-mailed statement.

In discussion forums on Microsoft's Web site, users report several issues with the e-mail client after installing the latest update. The trouble includes inaccessible address books, problems opening and sending messages in the "unsent messages" folder and trouble using templates.

The patch for Outlook Express fixes a problem in the way the application handles Windows Address Book files. Opening a specially crafted WAB file can result in execution of malicious code, giving an attacker control of the Windows PC, Microsoft said last week in Security Bulletin MS06-016.

Other patches that have given some users headaches are a comprehensive fix for Internet Explorer, which can break some Web applications, and an update for Windows, which can cause trouble on computers that run certain Hewlett-Packard photo-sharing software or the Kerio firewall.