This is a generic error and could be caused by a few things, but it's usually one of these:

1) Access a URL directly in the control panel instead of using the links.

2) Logging into multiple accounts without logging out of the first.

3) Using the back button

If it is, the fix is to logout so that it clears the session and then log back in.

https://cp.voipwelcome.com/logout

If that doesn't resolve it for you, contact reseller@voipo.com for assistance.