I am doing a project using android studio.Recently it showed an error that your SDK is missing or out of date
so, I downloaded SDK once again.Now it shows an error
I had the same problem, The answer is there : https://developer.android.com/studio/build/build-cache.html?utm_source=android-studio#clear_the_build_cache
You have just to do in a Terminal (for have terminal : Select View > Tool Windows > Terminal) :
On Windows:
gradlew cleanBuildCache
On Mac or Linux:
./gradlew cleanBuildCache
And build Gradle