Warning: array_key_exists() [function.array-key-exists]: The first argument should be either a string or an integer in /your-sitepath/wp-includes/category-template.php on line 176
– This problems stems from line 176 as stated above. The simple fix is to make sure the first argument is a string, to do this we will rap it in double quotes.
Change line 176 from:
Just add single quotes around the first $category variable which will fixed the issue.