Errors Saving and Checkin In Excel/PowerPoint files in SharePoint using CAC Card
Users accessing SharePoint using a CAC card may experienced problems with saving and checking in Excel and PowerPoint documents on the SharePoint servers. When attempting to do either a dialog box appeared stating that "The web server is currently busy please try again later."
-SharePoint 2007 SP2
The problem turned out to be that a setting, uploadreadaheadsize, is defaulted to 48kb. This is not big enough for the website to read in the entire header when a CAC certificate is added to it. To fix the problem I completed the following steps.
1. Start->Run-> runas /user:Administrator cmd
2. appcmd.exe set config -section:system.webServer/serverRuntime /uploadReadAheadSize:"200000000" /commit:apphost
This updates IIS to ensure it can read all the data in the headers.