I've also been seeing a lot of XPCD errors on my machine. This is how the XPCD errors would appear in the Console:
xpcd[224]: Info.plist does not contain an XPCService dictionary: /System/Library/Frameworks/Security.framework/XPCServices/SecurityAgent.xpc
This was driving me crazy, but I figured out how to fix it on my 2013 Macbook Air on OS X 10.9.4. Use at your own risk.
Any comments are welcome!
How to fix XPCD errors in OS X 10.9 Mavericks
DISCLAIMER: Editing system files and using the sudo command can be dangerous if done improperly. I am not responsible for any damage or data loss that may occur on your machine from following this procedure. Use at your own risk.
!!For some reason the Apple Community forums is adding a space in 'Contents'... Not sure why. This makes the commands fail. Remove the space. Posted correctly here: http://goo.gl/Z3KwGi!!
1. Open Terminal
2. Backup the /System/Library/Frameworks/Security.framework/XPCServices/SecurityAgent.xpc/Con tents/Info.plist file. This command will make a copy of the file on your desktop in case anything goes wrong:
cp /System/Library/Frameworks/Security.framework/XPCServices/SecurityAgent.xpc/Con tents/Info.plist ~/Desktop/Info.plist
3. Enter this command to add the XPCService dictionary to the SecurityAgent.xpc Info.plist:
sudo defaults write /System/Library/Frameworks/Security.framework/XPCServices/SecurityAgent.xpc/Con tents/Info.plist XPCService -dict-add ServiceType System
4. Next convert the plist back to the XML it was originally in with this:
sudo plutil -convert xml1 /System/Library/Frameworks/Security.framework/XPCServices/SecurityAgent.xpc/Con tents/Info.plist
5. Finally make sure the permissions are how they were originally by running these commands:
sudo chown root:wheel /System/Library/Frameworks/Security.framework/XPCServices/SecurityAgent.xpc/Con tents/Info.plist
sudo chmod 644 /System/Library/Frameworks/Security.framework/XPCServices/SecurityAgent.xpc/Con tents/Info.plist
6. Restart your computer for good measure. If all went well, the XPCD errors should be gone from the console.
For ease, here are the commands listed above in a single block:
cp /System/Library/Frameworks/Security.framework/XPCServices/SecurityAgent.xpc/Con tents/Info.plist ~/Desktop/Info.plist
sudo defaults write /System/Library/Frameworks/Security.framework/XPCServices/SecurityAgent.xpc/Con tents/Info.plist XPCService -dict-add ServiceType System
sudo plutil -convert xml1 /System/Library/Frameworks/Security.framework/XPCServices/SecurityAgent.xpc/Con tents/Info.plist
sudo chown root:wheel /System/Library/Frameworks/Security.framework/XPCServices/SecurityAgent.xpc/Con tents/Info.plist
sudo chmod 644 /System/Library/Frameworks/Security.framework/XPCServices/SecurityAgent.xpc/Con tents/Info.plist
Hope this helps.