On testing Mavericks I started seeing the above prompt when logging in.

I reached out to the MacEnterprise & JAMF Nation communities & it appeared that this window would appear when logging into a domain account on a Active Directory bound Mac.

Off I popped to http://bugreport.apple.com, & filed Bug ID# 15339910, & an Apple Engineer replied after a couple of days with the below:

Starting with 10.9, MCX will attempt to contact an AD/OD/MDM server during login, before the Finder is launched to ensure that all managed settings are applied before any user session applications run.

The dialog you are seeing comes up if this process takes more than a couple seconds.

The dialog does not add any time to the login process.

It’s just telling you why the login is taking extra time.

If your AD/OD/MDM server is responding slowly, then this is “normal” as the client just has to wait for the operations to complete.

So essentially, this is correct & new behaviour.

I was happy to leave it there, but was offered the below as ways of obtaining logs to troubleshoot further:

If you want us to diagnose the problem further, please enable MCX and MDM debug logging via:

sudo defaults write /Library/Preferences/com.apple.MCXDebug debugOutput -2
sudo defaults write /Library/Preferences/com.apple.MCXDebug collateLogs 1
sudo touch /var/db/MDM_EnableDebug

Restart and reproduce the problem, check the below logs:

/Library/Logs/ManagedClient/ManagedClient.log
/var/log/system.log

To stop the debug logging, remove the /var/db/MDM_EnableDebug and /Library/Preferences/com.apple.MCXDebug.plist files and reboot the machine

If, however, you wish to disable the prompt. Then the ever helpful Rich Trouton has a post on it here.