arcobjects - "Item not found in this collection" when trying to set the Shape on IFeatureBuffer

I'm working on code to open a 3rd party data file and convert it into a collection of features in a custom layer based on FeatureLayer. I have had no issue importing the data itself (nodal data for each 'cell' as a feature, such as elevation).

Because the data files are on average rather large (10k+ cells), I'm using a cursor implementation with an IFeatureBuffer that is filled with each cell one at a time. However, when I try to set the geometry of the cell via IFeatureBuffer like so,

IGeometry cellGeometry = getCellGeometry(cell);

featureBuffer.Shape = cellGeometry;

I subsequently get the error "Item not found in this collection" called on the second line. My first thought was that I was creating the cell geometry incorrectly in some way, so I tested it by creating a simple point as the geometry. This failed with the same error. I next thought it might be an issue with ZAware. I tried setting it to both ((IZAware)cellGeometry).ZAware = true; and ((IZAware)cellGeometry).ZAware = false; with the same issue both times.

I'm thinking it might have to do with how the fields in the FeatureClass were setup, but I'm quite stuck at the moment.

UPDATE:

I've tried updating how the fields are created to fix any issues that may exist therein, and the issue remains. The fields are generated like so,

    {
        if (this.ImportedField == null)
        {
            return null;
        }


        IObjectClassDescription fcDesc;
        if (this.DatasetType == esriDatasetType.esriDTTable)
            fcDesc = new ObjectClassDescriptionClass();
        else
            fcDesc = new FeatureClassDescriptionClass();

        IFields fields = fcDesc.RequiredFields;
        IFieldsEdit fieldsEdit = (IFieldsEdit)fields;


        //Setup shape field
        IField shapeField = fields.Field[fields.FindField("Shape")];
        IFieldEdit shapeFieldEdit = (IFieldEdit)shapeField;
        shapeFieldEdit.Name_2 = "SHAPE";
        shapeFieldEdit.AliasName_2 = "SHAPE";
        shapeFieldEdit.Type_2 = esriFieldType.esriFieldTypeGeometry;
        shapeFieldEdit.Length_2 = 0;
        shapeFieldEdit.Precision_2 = 0;
        shapeFieldEdit.Scale_2 = 0;
        shapeFieldEdit.IsNullable_2 = true;

        shapeFieldEdit.Required_2 = true;
        shapeFieldEdit.Editable_2 = true;
        shapeFieldEdit.Domain_2 = null;
        shapeFieldEdit.DomainFixed_2 = true;
        shapeFieldEdit.GeometryDef_2 = BuildGeometryDefinition(BuildGenericSpatialReference(true), esriGeometryType.esriGeometryPolygon, true, false);

        var fieldNames = this.ImportedField.CoordinateData.ScalarData.Select(nodeData => nodeData.Name).ToList();
        fieldNames.AddRange(this.ImportedField.CellData.ScalarData.Select(cellData => cellData.Name));

        //Add fields from ImportedField

        foreach (var fieldName in fieldNames)
        {
            IFieldEdit fieldEdit = new FieldClass();
            fieldEdit.Length_2 = 1;
            fieldEdit.Name_2 = fieldName;
            fieldEdit.Type_2 = esriFieldType.esriFieldTypeSingle;
            fieldsEdit.AddField(fieldEdit);
        }

        return fields as IFields;

    }

Answer

Finally found the solution. For whatever reason, the Shape field must be set before any of the other fields.

This does not work:

IGeometry cellGeometry = getCellGeometry(cell);
featureBuffer.Shape = cellGeometry;

But for some reason this does:

featureBuffer.Shape = cellGeometry;
IGeometry cellGeometry = getCellGeometry(cell);