So I got this error:
Warning: Cannot modify header information - headers already sent by (output started at ***/wp-content/themes/blankslate/functions.php:1) in ***/wp-includes/pluggable.php on line 876
when I activated the Gravity Forms plugin. Tried it with a few other plugins, too, same problem.
I've already checked functions.php, pluggable.php, and wp-config.php for leading/trailing whitespace. The error only comes up when I try to activate a new plugin. Any ideas?