New Post: Assembly reference error

Hi,

I'm sure this is something really obvious but I haven't been able to work this one out.
I have a Composite website that works perfectly on development, but on the live server (which has ASP.NET 4 enabled), I get this error. This is part of the Composite Contact form that I downloaded from the packages area.

Compiler Error Message: CS0234: The type or namespace name 'Core' does not exist in the namespace 'Composite' (are you missing an assembly reference?)

Source Error:
Line 8:  using Composite.Core.WebClient.Captcha;

Would this indicate an issue with permissions? (such as full access not being enabled) or would this be indicative of something else?

Thankyou in advance for your assistance.
Bron