Google has updated quite a few apps today. One of those is Google Voice. It’s a bug fixing update, but it’s a pretty significant one. It fixes delayed SMS notifications and inbox syncing issues. The inbox syncing issue caused duplicate notifications because they were not being cleared on other devices when you checked them on one. All this is fixed now, and the app should run fine. Hit the source link to update the app, or open the Play Store on your device(s).
Apparently I have carrier support issues (Verizon?) so can't really use Google Voice, I checked the "help" but I can't find anything.
I use Verizon and Google Voice with no problem. If the error you're having is with voicemail, activate voicemail on the Google Voice site and follow the instructions. It's pretty straightforward.