Craig Stuntz has written an extensive (in my opinion) blog post on troubleshooting this exact error message, I personally would start there.
The following res: (resource) references need to point to your model.
<add name="Entities" connectionString="metadata=
res://*/Models.WraithNath.co.uk.csdl|
res://*/Models.WraithNath.co.uk.ssdl|
res://*/Models.WraithNath.co.uk.msl;
Make sure each one has the name of your .edmx file after the "*/", with the "edmx" changed to the extension for that res (.csdl, .ssdl, or .msl).
It also may help to specify the assembly rather than using "//*/".
Worst case, you can check everything (a bit slower but should always find the resource) by using
<add name="Entities" connectionString="metadata=
res://*/;provider= <!-- ... -->
