Virtualbox (current version 5.0.10) is free software for creating virtual machines, VMs. These are other computer operating systems and programs running in a self-contained window on your operating system.
Avira 15.0.15 is a free antivirus software that I’ve used for years.
The long and short of this post is that there is a conflict with these versions causing error messages to pop up.
The workaround is to do nothing. That’s right, nothing. In a few minutes the you’ll get an error message.
Just leave it alone. Then, you’ll get another error message that looks the same. Leave it alone too. Resist the urge. Don’t hit OK.
In another couple of minutes, your VM will pop up and start running.
After you’re finished, shut down your VM and close the error boxes by hitting OK.
The Avira forums say it’s their conflict and they will fix it. Someday. Until then, it’s just wait or install another antivirus.