Microsoft has launched a public beta program for a major update to its Windows Home Server product that, in addition to other enhancements, is designed to fix a serious bug that could result in lost files.

Microsoft isn't putting a specific timeframe on the beta program, but said it hopes to have a final version of Windows Home Server, Power Pack 1, available by early June. "We intend to allow adequate time for feedback and thorough testing during the beta process," Microsoft officials said in a post Thursday on the Windows Home Server team blog.

The bug, a known issue in the product since at least March, can corrupt files, such as applications, music tracks, or digital photos, if they're transferred to a Windows Home Server unit equipped with two or more hard drives. The glitch can occur if the files are transferred using a number of specific Microsoft programs, including Vista Photo Gallery, Office OneNote 2007, Outlook 2007, and Money 2007.

Microsoft insists it's seen "only a very small percentage of users with confirmed instances of this issue," according to a statement the company released on the issue earlier this year.

Microsoft said the fix is taking so long because the problem presents no easy solution. "It is at an extremely low level of the operating system and it requires thorough testing to ensure that the fix addresses the issue," according to another blog post.

The note cautions that issuing a patch may take longer than until June. "That date could change as testing progresses," the post said.

In the meantime, Microsoft is telling potentially affected users to set Windows Home Server's Shared Folders setting to read only and to avoid using media management programs, including Windows Media Player, to import files to the server.

They should "also avoid redirecting applications to access files that are stored in the Shared Folders because some applications may change the metadata of a file without explicit user action," Microsoft said.

Windows Home Server allows consumers to create a central repository for all the digital content in their homes. Microsoft released the product in November.