When called from Acrobat X to edit an image, Photoshop CS6 cannot save the image

When called from Acrobat X to edit an image, Photoshop CS6 cannot save the image due to problems with the scratch disk, reporting "Could not open a scratch file because the file is locked, you do not have necessary access permissions, or another program is using the file. Use the ‘properties’ command in the Windows Explorer to unlock the file."
Used on its own, Photoshop does not have this problem. Also, if I change the image processor in Acrobat X to Photoshop CS5, there is no problem.