The issue arises when a user installs the SP3 update after having previously installed the first beta release of IE 8. Upon attempting to install the recently-released Beta 2 version of the browser, the user will be left unable to revert either IE 8 or Windows XP to any previous release.
Users will still be able to install future updates, and the company said that the problem only arises when the user has installed XP SP3 after installing the first IE 8 beta.
To avoid the issue, the company recommends that XP users who have installed SP3 after the IE 8 beta 1 release manually uninstall the browser.
Users running Windows Vista, Server 2003 and Server 2008 are also being advised to manually uninstall the first IE 8 beta before updating as well, though those systems are not said to be affected by the downgrade issue.
Microsoft released the second beta version of IE 8 yesterday. The new incarnation of the browser sports built-in malware support and a privacy feature designed to protect a user's browsing history and cookie data.