crop fails (temp image of 0kb created)

Hi, this is the first trouble I’ve had with the plugin:

I’m finding that the plugin goes through the motions of cropping my image (throws no errors) but in fact, the image is not cropped at all.

When I examine the uploads directory via FTP, I see that the timestamp for all thumbnail sizes matches the original upload time, and there is a temp file called scissors347ztc3 (random string) for each cropping attempt. The permissions for the temp files are 600, but my directory is 755, and all the other files are 644 (maybe thats normal for a tmp file?)

I suspect it may be a hosting issue, but I can’t see why! All my sites are hosted in a reseller account, and other sites are working. Time to isolate conflicts..

Any suggestions gratefully received!
Tx, Tim

http://wordpress.org/extend/plugins/scissors-watermark/