I applied SUPEE-6788 patch on magento 1.9.1 and now blocks on homepage disappeared. Here https://magentary.com/kb/cms-pages-transactional-emails-broken-after-supee-6788-patch/ they say go to System > Permissions > Blocks menu on admin but there is no such item on my admin menu, only "Users" and "Roles".
Seems like the new files introduced by the patch are not readable. Please check file permissions and ownership in app/code/core/Mage/Admin
Don't forget to clean the cache afterwards.