The problem is caused by a lack of memory for the Oyejorge Less compiler (which is used by Magento 2) or for other Magento 2 components.
The memory is limited by the .htaccess and the .user.ini files used by Magento 2.
###How to fix the problem
Increase the memory limit (e.g., up to 2048M) in the following places:
1. .user.ini
2. .htaccess (2 places)
3.pub/.user.ini
4. pub/.htaccess (2 places)