When I save for web as a jpeg it comes up with error Could not write the file not enough scratch memory available. I've boosted the memory usage to 89% and same error still
The memory slider is your RAM. Scratch disk is disk space on your hard drive. How much space is free on the drive used for scratch?
Make sure that you update to Photoshop 2017.1.1 (just released). That version includes a fix for a scratch space issue.