It may take a long time to log on to a Windows Vista-based computer that has antivirus software installed, and you may notice that the file size of the Setupapi.app.log file is very large
You have antivirus software installed on a Windows Vista-based computer. When you start the system, it may take a long time to log on to the computer. If you examine the Setupapi.app.log file in the %SystemRoot%Inf folder, you may notice that the file size is very large. Additionally, the size of the Setupapi.app.log file continues to grow every time that you start the computer.
Note: Any log file of 5 megabytes or more is considered large in this article. Additionally, there are several Setupapi related log files in this article.
For more information on this issue, including potential causes, workarounds, and resolutions, see: Microsoft KB Article KB958909.