no edit operation in progress

Using a versioned SDE layer that is part of a geometric network. Edit session is started in ArcMap and also started StartOperation. Then modified the geometry of a feature and call the store method. When "Store" method is called to save geometry, above message (No edit operation is in progress) is returned. Environment is C#Net in ArcGIS 9.3.1. Once again if i try to call the store method in exception, it is allowing and saving the feature with modified geometry.

Question is: What is the exact error here and why the same error not coming for second time store.