Error when calling IIndexQuery2.Within

Using a street centerline feature class and a polygon feature class, I am taking the shape of a street polyline and attempting to get all of the polygon shapes that this polyline is within. I am using IIndexQuery2.Within(feature.shape), and I DO have an index built on the polygon layer. When I pass in different polyline shapes, sometimes I get results and sometime an error is thrown. The error is:

Exception: System.Runtime.InteropServices.COMException (0x80041538): Exception from HRESULT: 0x80041538
at ESRI.ArcGIS.Carto.FeatureIndexClass.IIndexQuery2_get_Within(IGeometry pShape)

I checked for null geometries in the polygon layer and there were none. What else could be causing this error?
Thank you!