Hi, I was hoping someone might be able to help, I have the above error when i try to upload a ztool I have been working on. I had been working on textures last time I had the tool open and there were a lot of layers of polypaint etc, I really dont want to lose all that work!! Can anyone suggest a way I can open the ztool!! Please! Ahhhh 
Rucy x
Zbrush has trouble opening tools that have too big a file size for your computer. If you increased the memory available for zbrush to use this can cause problems. Saving files with subtools on high divide settings, lots of morph targets, lots of layers sounds like you might have saved the file and it is too big to open again. Trying to open the file on a bigger computer might not do the trick. I found that this is when incremental saving is your saviour.
Sorry I couldnt be more help. Hopefully you will get more aid.