There are several times that you will see this messages in your virtuemart admin. Solving the problem is quite easy:
- Enable the "Enable Multivendor (experimental only for developers" in Virtuemart configuration.
- Go to shoppers and you will see that a new column under the name Vendors exist.
- Allow only one user to be Ventor by disabling the others.
- Go back to configuration and disable the Multivendor ( set it to no )