WordPress image upload “failed to write to disk” urgent!

Image upload has worked well for months. Suddenly, I get “failed to write file to disk” though nothing has changed. Read the forums and worked with my hosting co to do the following:

Checked the php.ini file to read: upload_tmp_dir=”/tmp”
It did, but host co suggested using a new tmp folder within images, so:
Changed “/tmp” to be a tmp folder inside wp-content/images
Permissions set to 777.
Restarted database.

What else can I do? My host co won’t help further since it’s my own installation of wp. My site is on a shared linux server. Anything else I can add?

I’m desperate, and grateful for any assistance!