virtualbox.org

I created a virtual machine (Ubuntu 64-bit) with Virtualbox version 4.3.16 (Windows 7 64 bit host), and after upgrading Virtualbox to the latest version (4.3.26), I can't start the machine anymore. I get the following error:
Failed to open a session for the virtual machine Ubuntu
Unable to load R3 module in VBoxDD.dll
GetLastError=1790 (VERR_UNRESOLVED_ERROR).

This happens with all builds after 4.3.16, I tried several. I can only start the machine again after I downgrade VirtualBox back to 4.3.16. Can anybody tell me how I can upgrade the machine, or work around this error and still start my virtual machine with the latest version of VirtualBox?

I already fixed it myself. It happens to be that I used UXStyle to patch my uxthemes.dll file in order to use custom Windows 7 themes. When I reverted this file back and started using Windows' own themes I could start my machines again. The only weird thing is, that it's only happening with VB later than 4.3.16...