I recently tried to run Xubuntu 12.04 on virtualbox 1.2.0.It was working fine.Then due to some bug in my head 🙂 tried to upgrade virtualbox to VirtualBox-4.2.0_RC3 from [here](http://download.virtualbox.org/virtualbox/4.2.0_RC3/yLA&sig2=3BGpmhcRHx590ScQlj40Jw). Now without uninstalling the previous version I installed it.It created problem.While running any Vms after installing extension pack it gave error \[**” failed to load vmmr0.r0 (verr\_ldr\_mismatch\_native)”**\].

This issue is intially I couldn’t solve.Later I solved the issue as following.
Remove virtualBox ,remove folders from Program Files then removing “C:UsersUSERNAMEAppDataLocalVirtualStoreProgram FilesOracleVirtualBox” {Need administrative privilege}

Now install VBox freshly and import the virtual image projects/Disks.