I am getting errors using any of the infragistics web controls, if I add a WebTextEdit control for example, with no properties set, I get:

Compilation Error 
Description: An error occurred during the compilation of a resource required to service this request. Please review the following specific error details and modify your source code appropriately. 

Compiler Error Message: CS0011: Referenced class 'Infragistics.WebUI.WebDataInput.WebTextEdit' has base class or interface 'Infragistics.WebUI.Shared.IProvidesEmbeddableEditor' defined in an assembly that is not referenced. You must add a reference to assembly 'Infragistics.WebUI.Shared.v4.3'.

Source Error:
[No relevant source lines]
Source File:    Line: 0 

There is a reference to 'Infragistics.WebUI.Shared.v4.3' in the project.

Really not sure what to try next...