Long story short, this error popped up when I was running an update in Manjaro using the Add/Remove Software program. As a result, the in-progress update failed, and I wasn’t able to get past it. Even after restarting my computer, restarting Add/Remove Software, I still ran into the same error. After some research, I discovered that apparently, somewhere along the way, one of my updates had gotten interrupted. (Which makes sense when your two year old son just goes around pushing the hard reset button (conveniently?) located on the front of my tower… or the glowing blue power button on my UPS… you get the idea.) So yeah, there was a solid chance a process or two was interrupted. Because of that interruption, there was a temporary file left in my pacman cache. Removing this incomplete temp file was solved as soon as that file was removed and the update was restarted.

Solved error with sudo rm /var/cache/pacman/pkg/*.part

Just as a side note, there is a similar error covered on my blog where Arch fails to build Nettle6