I am getting the same error. It shows up when the Adobe Application Manager tries to update itself (on my machine at least). The full message is "There was an error updating. Please quit and try again later. Error Code: U43M1D207". I've been getting this or "unable to contact server" for a week now, so trying again later has not been successful!
Can you try updating the Adobe Application Manager by downloading the installer directly from our download page - http://www.adobe.com/downloads/?promoid=JZEFS? You can locate the Windows and Mac version towards the bottom right hand corner of the page.
Alternately you can review the installation logs for the update by following the steps listed at Troubleshoot with install logs | CS5, CS5.5, CS6 - http://helpx.adobe.com/creative-suite/kb/troubleshoot-install-logs-cs5 -cs5.html.
Downloaded Application Manager from the link provided. I have a mix of CS4 through CS5.5 apps and this was a CS6 download, don't know if that makes a difference but the application manager icon is not showing up in the notification area any longer asking me to update it and then failing. So I guess it fixed it.
Thanks, directly downloading the latest Adobe App Mgr as you suggested fixed the update error for me. I got the error after a new install of CS6 (had left CS4 installed), but now all is working well.