It is the case of a compatibility and reliability update for Vista RTM, re-released on May 21, 2008, well after Microsoft wrapped up with Service Pack 1.

"This update resolves some compatibility issues and reliability issues in Windows Vista. By applying this update, you can achieve better reliability and hardware compatibility in various scenarios," reads Microsoft's description of KB938194 which is offered in both 32-bit and 64-bit versions for the respective editions of Windows Vista Service Pack 1.

In the fall of 2007, the Redmond company issued two Vista compatibility, performance and reliability update packs that were essentially bits of the first service pack, but offered to Vista RTM users almost half a year ahead of SP1 via Windows Update. Following the availability of SP1, Microsoft informed that there are users who cannot implement the service pack due to a variety of issues, but mainly incompatibility problems. For them, the KB938979 and KB938194 update packages were reissued. Users of Windows Vista SP1 need neither of the packs.

According to Microsoft, KB938194 will resolve the following problems:

"The screen may go blank when you try to upgrade the video driver.
• The computer stops responding, and you receive a "Display driver stopped responding and has recovered" error message.
• The computer stops responding or restarts unexpectedly when you play video games or perform desktop operations.
• The Diagnostic Policy Service (DPS) stops responding when the computer is under heavy load or when very little memory is available. This problem prevents diagnostics from working.
• The screen goes blank after an external display device that is connected to the computer is turned off.
• There are stability issues with some graphics processing units (GPUs). These issues could cause GPUs to stop responding (hang).
• Visual appearance issues occur when you play graphics-intensive games.
• You experience poor playback quality when you play HD DVD disks or Blu-ray disks on a large monitor.
• Applications that load the Netcfgx.dll component exit unexpectedly.
• Windows Calendar exits unexpectedly after you create a new appointment, create a new task, and then restart the computer.
• Internet Connection Sharing stops responding after you upgrade a computer that is running Microsoft Windows XP to Windows Vista and then restart the computer.
• The Printer Spooler service stops unexpectedly.
• You receive a "Stop 0x0000009F" error when you put the computer to sleep while a Point-to-Point Protocol (PPP) connection is active."