I tried a fresh install with new files and a new database, but I continue to encounter this error. Help
 

This is likely a write issue on your server. Please have your hosting provider or server administrator ensure that PHP can write to the /uploads folder and create new folders/files. 

I took care to set the value 777 for all the subfiles and files in my FTP

Unfortunately, that may not be correct. Depending on your server configuration, that can actually prevent files being written to. Checking with your hosting provider or server administrator to ensure PHP can write would be the first step if you are unsure how to do this correctly.