This error is annoying and seemingly hard to find a way to fix it.
I got it will Eclipse Luna (4.4.1) and the latest SDK and ADT.
After much messing around – I found the way to fix is to remove Android SDK Tools. SDK Platform-tools and Build-Tools (you might not need to remove al three but I tried platform-tools by itself and it didn’t work)
and then re-installed them. Restart Eclipse and the error should be gone!