After a recent update of MAMP on my system, I was no longer able to load Magento sites on my localhost. The problem seems to be a PHP compatibilty issue and the solution is pretty simple.
Loading up Magento sites on my local development server, I found myself greeted with a page saying:
Can’t retrieve entity config: core/store_group, followed by a long trace: message and
I found the solution online here: dltr.org and I’m posting it on my blog to make it easier for me to find later on!
Download a new copy of Magento from the Magento Commerce site and unzip the file.
Open Magento > lib > Varien and copy the Simplexml directory, then navigate through your sites on your localhost to the same location and replace the directory by pasting and overwriting.
Restart MAMP (or XAMP, LAMP, WAMP etc) and reload your sites.
Thanks to Damodar Bashyal for this!