My Android development environment(Eclipse) start making an build error like this from one day:

Unable to build: Could not find dx.jar file

I found solutions like uninstall and reinstalling ‘Android SDK Platform-tools’ and performing a clean build, but it didn’t work.

Also, when I tried to install Android API 17, this kind of error occured:

'Installing this package also requires installing: - Missing SDK Platform Android, API 17'

By googling, someone solved this problem by performing ‘Clear Cache’ from the Android SDK Manager preferences, and reloading the packages.

After that, I could install updated Android SDK Platform-tools, and then the problem solved.