From digging in to the error you supplied, it looks like this might be a known issue with the VMware VDDK 5.1. In the release notes for VDDK 5.1, they have the following entry:
Whenever vCenter Server does not provide an SSL thumbprint for the target host, the VDDK library might core dump in the function VixDiskLib_Open(). This could happen (but does not always happen, depending on memory content) when vCenter Server 5.1 manages virtual disk on ESXi 5.0 and older hosts. A fix has been identified, and will be available in the VDDK 5.1 first update release.
It appears that the code base that VDP is based off of exposes this issue. If you are using VC 5.1 and ESXi 5.0 the suggested workaround is to upgrade to 5.1.
Does the VC / ESXi configuration apply to your situation?