Word couldn't send mail because of MAPI failure Unspecified error

Gmail is my only eMail program.
When I have Word document I do following
File > Save&Send > Send using email > Send as attachment
I get error
Word couldn't send mail because of MAPI failure:"Unspecified error".
This error can occur if you attempt to send a Word document as an e-mail attachment in Word and the MAPI session was closed and Word is no longer able to connect to that MAPI session.
It can also occur if there is a problem with the fax configuration.
To correct a MAPI related error: restart the MAPI e-mail program (for example,Outlook) or save and close the document, and then restart Word after restarting your MAPI e-mail application.
Word will establish a new MAPI session, allowing the document to be sent.
I tried having gmail open in the background, but got same result
How do I fix this ?

what is a MAPI compliant mail client ?

what is a example of a MAPI compliant mail client ?

thank you