If you have encounter this error on S5 and have already follow all of the instruction on the (Gmail - Google Mail with System Five Solution Article) and still isn't working.
You may have an issue with your mapi32.dll (MAPI)
In order to fix this issue you will need to install Thunderbird Email for the system to also reinstall the mapi32.dll
After the installation of the thunderbird you can just remove it after .
Test the System5 if you can send emails.