One quick solution I prefer which I suited most for this situation is simply delete .metadata folder of your work space and import your projects again. If you try all other option it wont guarantee the success. Sometimes the above solutions work sometime you will spend your precious hours to fix this configuration.
One day i decided to clean my work station.I arranged the projects to their suitable folders according to different clients. As a result all got messed up. After spending a whole day it did not end up in a fixed work space. Next day I simply deleted the .metadata folder of the work space and imported all the projects again. Bingo all set.