I forwarded your info to our support team so they can help troubleshoot.
In the meantime, the help for the SendEmail command shows this for your -58 error:
-58 = No data received. May have timed out if no response in 10 seconds. Check I/O unit power.
Do you have an especially slow connection to the internet, where it might take longer than 10 seconds to get a response from a remote server?
Also, do you have an email server besides gmail you could try? Gmail has made changes to their security requirements which have been messing up a lot of people. Did you check that email account to see if gmail sent you any security warnings? (Sometimes you have to click on something to say: “yes that’s really me,” for example.)