Take a look at the first "more like this" link to the right of these messages.
The error code U44M2P28 means “Update not applicable”.
Either you’re already running 6.1.1 or you need to apply some of the intermediate updates between whatever you have now and 6.1.1 which is the current version, although I’d expect a LR 6.2 at some point.
Do a help / System info and find the precise version of LR 6 you’re running then download and apply all the updates after that in order. You can get them from here:
The sequence of versions since LR 6 is: 6.0, 6.0.1, 6.1, 6.1.1.
I had the same message as Kevin and others. Fairly early on after product release, I installed Lightroom 6.0 on my Mac (OS 10.10.5 Yosemite). I have done no LR updates since then. Today when I tried using the Update function in the Help Menu, no updates for LR were found, just some Camera Raw updates. Then when I went directly to the Adobe web site to get the update patches (link below), the updates to LR 6.0.1 and LR 6.1.1 failed. I did not try LR 6.2 because I understand there may be some usability issues according to some bloggers. To make a long story short, here is what I did to get a successful update to LR 6.1.1:
1. Uninstall LR 6.0 using the uninstall application in the LR folder in Applications. Do not check the box to remove preferences.
2. Reinstall LR 6.0 using the install package from the original installation (Lightroom_6_LS11.dmg). If you don't have this package, you can download it at:
Download Photoshop Lightroom . Click the Application Installers: Mac OS X, Downloads.
3. After installation, open LR and provide the necessary Product Serial Number.
4. Quit LR.
5. From the Adobe site (Download Photoshop Lightroom) download the patch Lightroom 6.0.1/2015.0.1
6. Apply this patch.
7. From the Adobe site (Download Photoshop Lightroom) download the patch Lightroom 6.1.1/2015.1.1
8. Apply this patch.
Perhaps steps 5 & 6 could be eliminated. I don't know. The above worked for me. What a pain in the back side.