Hi.
I’m having the same issue. I use Bluehost, and I checked with them. Bluehost does not have/use modsecurity either. On their end, in addition to seeing the same error, they also received an error that said ‘php cannot modify header ozhgradient.php line 100’. Hope this helps. Please let me know when this is resolved – I would really like to be able to use the plugin!
