Thanks for your reply. I have the SOESupport dll in
C:\Program Files (x86)\ArcGIS\DeveloperKit10.1\bin and it was already in the bin directory of the sample. I should have mentioned that initially I got a different error, then added a reference to SOESupport.
I don't have it in the GAC though and ArcGIS Server is not installed on the machine. So maybe that's the issue...