BizTalk 2010 Setup fails at SSO Install.

While installing the recently released BizTalk 2010 Developer Edition, I ran into an unexpected installation error.

The Enterprise Single Sign-On installation failed complaining that it was unable to 'find the path specified'.

Manually installing ENT SSO from the \BT Server\Platform\SSO64 did not do me much good; the installation failed as stand-alone also.

In the end I found that the problem was that I was installing from a network location, even though it was mapped to a drive letter.

To be exact: I was installing onto a VMWare Windows 2008R2 64-bit image, mapping a shared folder on the host holding the installation files.

I have found that there are two ways that will get you out of this:
1) Create an ISO and mount it from the VMWare image as CD.
2) Copy it to a virtual disk local to the VMWare image.

Problem solved.