So I had to make a script to transfer some files over the network using Robocopy. And the password has an ampersand in it, so Robocopy parsed the password into a new command. D'oh!
Some documents say prepend the & with ^ (^&). Some say surround in double quotes ("&"). The error message Powershell gives you is to wrap in double quotes. It even shows you an example! ("&")
But it is wrong. In Powershell you have to wrap the ampersand in single quotes ('&').
net use \\TO_DOMAIN_OR_IP\g$ /user:TODOMAIN\TOUSER pass'&'word
robocopy c:\backups\folder\ \\TO_DOMAIN_OR_IP\c$\backups\ /Z /MIR