Upgrade to new macOS Mojave
You get an error of:
The document "" could not be opened because of a disk related error while making the temp file. (Error code - 123, The disk volume does not support Macintosh "safe saving". MoneyWorks cannot use it.)
if you try running an older version of MoneyWorks on a new macOS Mojave, you should upgrade the software before upgrading the operating system.
Alternatively, you may switch to MoneyWorks Now, a cloud-based accounting system which always has the latest version without you having to worry about upgrading the computer.
Contact your consultant on upgrading MoneyWorks.