creating a quiesced snapshot failed because the (user-supplied) custom pre-freeze script in the virtual machine exited with a non-zero return code

There is a bunch of stuff on the internet, but the one that really helped me out was from Duncan Epping on Yellow-Bricks.

To sum it up, you need to add the flag -Q 0 to the parameters. This is an undocumented flag that actually prevents VCB from trying to execute any pre/post scripts. The root cause is a bug in VMware tools that should be getting fixed in an update so they say.