I am using LR 6.8 for Mac (perpetual license) that I purchased through Amazon. I am not using CC. I am having problems updating to 6.12 from 6.8. It shows this error message: "Update is not applicable. Error Code: U44M2P28". Also, CC Apps is showing that I am already up to date, but when I check with my LR, it shows that I am still using 6.8. Please advise with specific instructions.
Try downloading the update manually from here and install it: Download Photoshop Lightroom
If it does not work, remove LR completely and reinstall.
The link above offers to download the 6.0 base installer as well as the 6.12 update - the install always is a 2-step process.