I'm having trouble uploading a logo .png file
Some servers that don't fully support the WordPress software, need additional settings in place for uploading. In this case, a user on a smaller hosting service was able to fix this error by adding:
"^multipart/form-data;" "MODSEC_NOPOSTBUFFERING=Do not buffer file uploads"
into an .htaccess file in
*We don't encourage our users, especially those who are new to hosting their own site, to make these changes on their own. We suggest having your server host tech support make these modifications to your site.