Microsoft Tuesday released a reliability update for Windows Vista Service Pack 1 (SP1) that fixes several bugs in the OS update, including one that threw off errors when users tried to run large applications, such as Microsoft's own Excel 2007 and Windows Media Player.

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The update, which Microsoft posted Tuesday to its download servers, will be pushed to users automatically next month via Windows Update, a company engineer said on a support forum yesterday.

Although Microsoft regularly issues reliability updates separate from its normal monthly security fixes, this is the first time it has released one specifically for Windows Vista SP1. Microsoft released Vista SP1 to the general public in late March.

Among the fixes included with the update is one that Microsoft characterized as an issue "in which large applications cannot run after the computer is turned on for extended periods of time," according to an accompanying description of the update's contents. "For example, when you try to start Excel 2007 after the computer is turned on for extended periods of time, a user may receive an error message that resembles the following: EXCEL.EXE is not a valid Win32 application."

Users reported the problem on a Vista support forum as early as April 1, claiming that they saw the error message when trying to run Office 2007 applications, including Excel and Access, as well as when launching Vista 's built-in screen capture tool and Windows Media Player.

Within three weeks, Microsoft engineers on the same forum thread had confirmed the bug and said the company was working on a fix. "The error messages are confusing, but the problem is neither an invalid application file nor insufficient system resources," said John Gray, who identified himself as a Microsoft employee. "It only affects certain applications, and typically only after the user has been logged in for an extended period of time."

Tuesday, Gray chimed in again to tell users the fix was tucked into the reliability update. "Thanks for your patience!," he wrote on the forum. "This should resolve this issue for those of you hitting it."

The SP1 reliability update fixed several other bugs, according to Microsoft's write-up, including crashes when using Apple Inc.'s QuickTime multimedia player, and stuttering audio and video high-definition playback on systems equipped with Nvidia network adapters.