Lucy's blog

When deploying a VS 2008 workflow developed in .net 3.5 to a server (w.o. 3.5) the workflow will not start, and the error log will say ‘System.Core’ not found.

To fix this: install .Net3.5 on your server.
http://www.microsoft.com/downloads/details.aspx?FamilyID=333325FD-AE52-4E35-B531-508D977D32A6&displaylang=en

Kudo’s again to Stef for finding this.