How are you trying to install it, and where do you get that error message?
Sounds like Apper/PackageKit. Apparently you install it by clicking on the downloaded package, and there is some conflict.
Use zypper or rpm on the command line instead, something like “sudo zypper in VirtualBox.rpm”, you should at least get a more detailed error message then.
Or use the 1-click install to install the openSUSE package from the Virtualization repo: http://software.opensuse.org/package/virtualbox-qt
(click on “Show other versions” and then “Show unstable packages” to see 5.0)