Disk2vhd : error during copy. The error could not be performed due to an I/O error

I'm trying to convert a fully patched, Windows Server2008 R2 system disk into a VHD by using disk2vhd from Microsoft Sysinternals.

Every time, the conversion fails with error during copy. The error could not be performed due to an I/O error, regardless of whether I sue the vhd or vhdx format, or whetehr I use the Volume Shadow Copy option.

I am a local administrator, running disk2vhd as administrator and have disabled the anti-virus on the server, but it makes no difference.

I see this event in the eventlog around the same time as the error, so I suspect they're related.

Volume Shadow Copy Service error: Unexpected error querying for the IVssWriterCallback interface. hr = 0x80070005, Access is denied. This is often caused by incorrect security settings in either the writer or requestor process.

Operation: Gathering Writer Data

Context: Writer Class Id: {GUID} Writer Name: System Writer

Writer Instance ID: {GUID}

What's the problem here, and why can't I get this disk converted?

Its stupid, but running chkdisk first (yes, even when you are getting no error messages or problems anywhere else) before running hd2vhd again has fixed this for us too many times.