UR SIM image file not working

Hello,
I have downloaded the UR SIM from the UR download section. Installed virtualbox, but I have issue to make the virtual machine with the UR SIM working.
Virtualbox is not able the virtual disk “vmdk” file from the downloaded package.
Thew error message is:
Failed to open the disk image file /home/dkr/URSIM_virtual/URSim_VIRTUAL-5.12.6.1102099.vmdk.

Could not get the storage format of the medium ‘/home/dkr/URSIM_virtual/URSim_VIRTUAL-5.12.6.1102099.vmdk’ (VERR_NOT_SUPPORTED).

Result Code: VBOX_E_IPRT_ERROR (0x80BB0005)
Component: MediumWrap
Interface: IMedium {ad47ad09-787b-44ab-b343-a082a3f2dfb1}
Callee: IVirtualBox {d0a0163f-e254-4e5b-a1f2-011cf991c38d}
Callee RC: VBOX_E_OBJECT_NOT_FOUND (0x80BB0001)

Any advice how to solve this issue?
Seems like the file in the package downloaded from UR site is corrupted.

Dusan.