We sent a big (2G) zipped web project to a client which we had no problem uploading to box.com in < an hour.

The client was able to download it, but now can't seem to transfer it to their server without the upload failing (last try @ 80% complete after ~6-hours). Is there some transfer method that supports resume in such a case (I don't even know what he's using, guessing sftp)?

What's their server? Bet it's going onto a FAT32 disk and failing at the file size limit  LMAO

(I used to use FlashFXP or something as my FTP/FXP client, I'm pretty sure that did resume uploads and that's at least 10 years ago)

Unlikely but possible. More likely is ntfs or some legacy unix fs. Dunno why the upload is so slow.

Poor Internet connection? (compared to yours)

Plenty give fuck loads of download but naff all upload bandwidth, I'm looking at you Virgin.

I'm pretty much in the dark about why/how they do stuff. Maybe it's best.

Maybe tell them not to use the bathroom while uploading?

rsync.