I overcame my problem by copying the Dynamic Content dlls from webroot\bin to webroot\MirroringService bin.  Not very elegant but it works.  I followed this blog post and I have mirroring working with a Staging server and 2 x Live servers sharing a single Live database.

Next problem - to make this work with each live site having a dedicated live database.  Any thoughts?

Hi, 

It should be fairly easy to setup this up (although I haven't tried it yet). You need to install mirroring services on all of three servers, staging and 2 live servers. Then create two channels at staging server pointing to live servers one each. Hope this helps.

Regards,

Thanks Shahid.  I was thinking along the same lines though I run into problems adding a second endpoint in the <client> section of the staging mirroring service web.config

Without seeing the config files and error message, it's hard to suggest anything :( Could you please paste the error message and staging web.conifg here if possible. Otherwise raise a ticket with developer support. (http://world.episerver.com/Support/Register-Support-Incident/) and will continue from that. 

I had the same problem with <dynamicContent> after updating the Alloy Tech sample with a new assembly name.  I found <dynamicContent> in the episerver.config file and, after updating the assembly reference with the new assembly name, the problem was resolved.