Frequent/regular "Could not open file for reading" error

[dibble]

Having real trouble getting S3D to consistently send larger files to my printer. I'm getting "Could not open file for reading".

Details: XYZ Duo 2.1.0 firmware
OS: OSX 10.11.6 (el capitan)

In the past, I've been able to save toolpaths to disk and manually run the g-code from the machine control panel when this happens (as opposed to just hitting the print/usb cable icon). But, now even that is failing. Depending on the .stl file I'm trying to print, the line number of the fail varies. But, in every case I get a checksum error: "CheckSumFail:PN:0" while the file is uploading to the printer.

The files that fail tend to be larger/taller. But, nothing crazy. As a matter of troubleshooting, I built a cylinder with a hole that seems to have trouble loading. I've attached it. That same cylinder without the hole sends fine every time.

It isn't predictable, either. The same file that errors out--with persistence--will eventually go through. But, I've restarted my computer, restarted the printer; checked the permissions on the temp directory and the directory I use for manually created .3w files to make sure they have read/write access for everyone.

I don't know if I've left out any pertinent details. But, this is getting frustrating. I was printing a job and one of the extruders jammed. Cleared and cleaned everything out, and now I've spent an hour trying to get that same job to even upload now. No different settings---the same .3w file as before that had already begun printing once.

Any ideas?