Using Python we update the source features for several network datasets and re-build them every night. The data is stored in SDE (MSSQL), and the Feature Datasets are registered as versioned. And the data is used in AGS routing services. Everything works fine, until I add a network attribute with a custom solver. Then editing the source features for any of the Network Datasets we have fails with a generic error message. If I delete the network attribute that uses the custom evaluator, everything works fine again. The custom evaluator is based on a sample from Esri, and works fine in action.