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File not found error


First of all I want to say that this project is an excellent idea and is just what we are after. I want to add a business data column as a site column so I can use it with content types so it is perfect for this.
I have managed to upload and deploy the assembly successfully.
When clicking on the address book icon (which I assume opens a search screen) I get the below error:
File Not Found. at MacroView.SharePointFields.clsBDCLookUpPicker.CreateChildControls()
at System.Web.UI.Control.EnsureChildControls()
at System.Web.UI.Control.PreRenderRecursiveInternal()
at System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint)
There are no errors in the event logs and I also couldn't find anything in the SharePoint logs relating to the error either.