I fixed the error!
I was having problems with this as well on my site https://www.lilaussieprems.com.au. I have been getting error messages that i have exceeded the database size etc. and ever since getting that message i lost the visual editor feature.
To fix the problem i just uploaded a new fresh copy of the tiny_mce_gzip.php and it’s working perfectly. If it wasn’t for cyzum’s post i would not have known which file to look at, so THANK YOU!!