Call your Google Voice number from some other number (NOT the other Google Voice number) and leave a voicemail message. Talk for at least 10 seconds so it isn't interpreted as a hang-up call.
Log into the correct Google account that hosts that Google Voice number, and go to the "Legacy" version of the Google Voice web interface. Look at the History tab. Is the call there? If not, you're looking at the wrong account. If it is there, look at the voicemails tab. Is the voicemail message there? If so, open a new browser tab and go to Gmail. Make darn sure you are looking at the SAME Google account that just received the message. Look in the inbox and spam folders, or look in the "All mail" folder (
https://mail.google.com/mail/u/0/?shva=1#all) to see if the note is there.
If you find the note, then you have no problem. If you don't find the note, then go back to Google Voice, Legacy mode, on this page:
https://www.google.com/voice/b/0#voicemailsettingsClick the "add a new email address" link and enter whatever non-Gmail email account you might have (any other email provider except Gmail). Test forwarding to that email address.