My daily SharePoint frustration - VI

The error:

Field type MyField is not installed properly. Go to the list settings page to delete this field. at Microsoft.SharePoint.SPFieldCollection.CreateNewField(String typeName, String displayName) at Microsoft.SharePoint.ApplicationPages.FieldNewPage.Save() at Microsoft.SharePoint.ApplicationPages.FieldNewPage.BtnOk_Click(Object sender, EventArgs e) at System.Web.UI.WebControls.Button.OnClick(EventArgs e) at System.Web.UI.WebControls.Button.RaisePostBackEvent(String eventArgument) at System.Web.UI.Page.RaisePostBackEvent(IPostBackEventHandler sourceControl, String eventArgument) at System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint)

What I was trying to do:
To create a custom field type.

The problem:
The assembly in the GAC did not have the class declared in fldtypes_XXXXX.xml. What happened was that I had multiple projects generating different assemblies, but using the same namespace.

The solution:
To organize the assemblies and namespaces, so that the reference to the custom field class is correct (that is, that the class in fact exists in the declared assembly).