Can't edit/save and existing product in Magento

Question

I'm trying to make changes to an existing product, such as adding images. I'm able to upload the image without error, and when I press "Save" it looks like it saves properly, but there is not green "success" indicator. When I re-open the product the image is not there. I tried changing the description and it doesn't save either. It seems that something is preventing me from editing an existing product in any way.

Here is what the system.log shows:

2015-09-19T17:41:34+00:00 ERR (3): Warning: array_key_exists() expects parameter 2 to be array, null given  in /home/username/public_html/app/code/core/Mage/Adminhtml/controllers/Catalog/ProductController.php on line 507
2015-09-19T17:41:34+00:00 ERR (3): Warning: array_key_exists() expects parameter 2 to be array, null given  in /home/username/public_html/app/code/core/Mage/Adminhtml/controllers/Catalog/ProductController.php on line 507
2015-09-19T17:41:34+00:00 ERR (3): Warning: array_key_exists() expects parameter 2 to be array, null given  in /home/username/public_html/app/code/core/Mage/Adminhtml/controllers/Catalog/ProductController.php on line 507
2015-09-19T17:41:34+00:00 ERR (3): Warning: array_key_exists() expects parameter 2 to be array, null given  in /home/username/public_html/app/code/core/Mage/Adminhtml/controllers/Catalog/ProductController.php on line 507
2015-09-19T17:41:34+00:00 ERR (3): Warning: array_key_exists() expects parameter 2 to be array, null given  in /home/username/public_html/app/code/core/Mage/Adminhtml/controllers/Catalog/ProductController.php on line 507
2015-09-19T17:41:34+00:00 ERR (3): Warning: array_key_exists() expects parameter 2 to be array, null given  in /home/username/public_html/app/code/core/Mage/Adminhtml/controllers/Catalog/ProductController.php on line 507
2015-09-19T17:41:34+00:00 ERR (3): Recoverable Error: Argument 1 passed to Varien_Object::addData() must be of the type array, null given, called in /home/username/public_html/app/code/core/Mage/Adminhtml/controllers/Catalog/ProductController.php on line 513 and defined  in /home/username/public_html/includes/src/__default.php on line 1019
2015-09-19T17:41:34+00:00 ERR (3): Warning: Invalid argument supplied for foreach()  in /home/username/public_html/includes/src/__default.php on line 1021

Answer 1

Clear your Magento cache.

It also looks like your running it compiled, you may need to re-compile Magento.

I recommend disabling Magento compilation as the feature has proven to be a bit of a problem with mixed results. In my experience, it causes more harm than good.