Array Flip Error Message on All Node Pages
Something is calling entity load with an incorrect $ids parameter.

This could be from something like node_load() or equivalent or node_load_multiple() or equivalent. If you pass in the wrong type of value into any of these you could end up with the error you mention.

If you want, add just above line 178 the line

print_r($ids);


Then reload the problem page and you will get a bunch of text print out.
Post the text back here (if you can upload files and there is a lot of output you could paste it in a txt file and post it).