Symbol 'SysTick_IRQn' could not be resolved
The proper solution, as explained In this FAQ entry
is to uncheck “Index unused headers” from the project properties (or workspace preferences) on the C/C++ Build >> Indexer page.
Unchecking “Renerate under root” just accidentally solve this problem but creates other problems (difficulty to manage your project under SVN or GIT or to add your own source and header files for example) that made it a less-than-optimal solution.
Bernard (Ac6)