Step 1. Check that your Settings (accessed from File -> Settings) match following screenshots or equivalent:

Step 2: Close IntelliJ

Step 3: Delete all .idea directory and .iml files in your repo:

rm $(find . -name *.iml)

rm -r $(find . -name .idea)

will delete all files recursively on mac. On windows use the simpler

dir *.iml /s

dir .idea /s

Step 4: Delete IDEA system directory. On Windows the IDEA system directory is C:\Users\username\.IntelliJIdea2016.2\system

On Mac do:

rm -r ~/Library/Logs/IntelliJIdea15/*

rm -r ~/Library/Caches/IntelliJIdea15/*

Resources:

http://stackoverflow.com/a/5905931/147530:

First of all you should try File | Invalidate Caches and if it doesn’t help, delete IDEA system directory. Then re-import the Maven project and see if it helps.