Apple Computer this week said it is trying to fix a problem that prevents its QuickTime media player from working with the most recent versions of Microsoft's browser. The problem cropped up on 31 July, when Microsoft released a service pack upgrade for Internet Explorer 5.5, dubbed SP2. Microsoft routinely issues service packs to patch security problems with its browser. In this case, however, Web surfers who installed the product were unable to view QuickTime video. The same problem affects a test release of Microsoft's new Internet Explorer 6 browser. "Apple is aware of the compatibility issue between QuickTime and the beta of Internet Explorer 6 and Internet Explorer 5.5 SP2, and we are working with Microsoft to resolve the issue," an Apple representative said in a statement. "There will be a fix for which more information will be made available shortly." Other popular software programs, including RealNetworks' RealPlayer, Adobe Systems' Acrobat Reader and Macromedia's Shockwave player, appear to work normally with the browser upgrades. The QuickTime compatibility problem comes as Microsoft is revamping its support of third-party Web applications from within the browser. At stake is the role of computer code known as "plug-ins", technology pioneered by Netscape Communications to extend the function of Web browsers by welding them closely to other programs. With IE 5.5, Microsoft discontinued support for plug-ins, according to a Microsoft representative. Instead, the browser relies on technology developed by Microsoft known as ActiveX that links desktop applications to the Web. ActiveX has been seen as a challenger to Sun Microsystems' Java programming language, which Microsoft has said will no longer be supported by default in its pending Windows XP operating system and IE 6. ActiveX has also been identified as a source of serious security risks, offering a powerful tool for malicious programmers to take control of a target computer, for example. As specific security problems have come to light, Microsoft has issued repeated service pack upgrades and patches for its browser. Numerous Web surfers who recently installed IE 5.5 SP2 complained in emails to CNET News.com this week about the sudden loss of their ability to view QuickTime files. "I ran into the problem myself today, when I tried to watch movie trailers at http://www.apple.com/trailers," wrote Kai de Leeuw, a Windows user from Stockholm, Sweden. "I just recently--two days ago--installed IE 5.5 SP2." Brad Mathis, a network security engineer from Evansville, Indiana, blamed the problem on Microsoft. "Being a security-conscious person, I try to stay updated with the latest service packs," he wrote. "Unfortunately, SP2 for IE 5.5 was a service pack with a hidden agenda. It may have had a security fix or two in it, but was also designed to remove non-Microsoft product compatibility." Others complained that they had difficulties undoing the installation to switch back to a version of IE that supports QuickTime. Limore Shur, president and creative director at New York-based design company Eyeball, said that Microsoft software support waived its usual fee after conceding there was no fix for the problem short of reinstalling IE from the original CD-ROM. "We are all left asking what should we do? Being a design company, we show all of our work as QuickTimes on the Web. If any of our clients upgrade (ad agencies or networks), they will no longer see our work," Limore wrote in an email. Windows XP lead product manager Jim Cullinan said a fix should be posted shortly. "We have been working with Apple to be sure QuickTime works--and they have developed a version that is compatible with IE 5.5 and 6.0," he said. News.com's Joe Wilcox contributed to this report. See the Windows News Section for the latest Windows headlines. See the Software News Section for full coverage. Have your say instantly, and see what others have said. Click on the TalkBack button and go to the Microsoft forum. Let the editors know what you think in the Mailroom. And read other letters.