Hello,
i´m on a mac (Mac OS X 10.7.5). If i start ZBrush 4R7 p2 i always get the message (File Write Error - Disk space is critically low…) and i´m not able to quit ZBrush anymore (Force Quit Application works). There is enough space on my disk so that can not be the error.
Before the p2 Version my ZBrush 4R7 does not launch at all. ZBrush 4R5 works fine.
It would be really nice if someone who has solved that issue can give a hint. 
Have a nice day!
wuji_4D
This sounds like permissions.
Go to your Macintosh hard drive and find the /Users/Shared/ZBrushData folder. Select that folder and press Cmd+I to get info on it. At the top of the window it should say “ZBrushData” and have a folder icon.
At the lower right corner of that window, click the padlock icon, then enter your admin name and password. If that icon isn’t visible, click on Sharing and Permissions to expand that section. It’s at the bottom of the window.
Now change the Everyone user group’s permission level to “Read Only” then click the gear icon underneath and choose “Apply to enclosed items.” You’ll need to confirm. Change Everyone back to “Read & Write” and then apply to enclosed items again. Click the padlock icon to lock permissions before closing the window.
This should resolve the issue.
Thank you for your help!
I´m sorry but that solution had not removed the problem. There is still a error message during startup.
Greeting
wuji_4D
Problem solved with patch 3 (ZBrush 4R7 p3)