I've attached a better image that shows I can delete the alleys feature class and I include an image showing that it is part of the network.
When I try running the following code from ArcGIS 10/Python on a File GDB:
arcpy.geoprocessing.env.overwriteOutput = 1
arcpy.Select_analysis(DP3LW_TRANSE_CENTERLINE, Temp_Transe_Alleys, "CLASS_CODE = 14")
arcpy.CopyFeatures_management(Temp_Transe_Alleys, DP3LW_Transe_Alleys, "", "", "")
arcpy.CalculateField_management(DP3LW_Transe_Alleys, "SPEED", "10", "VB", "")
I got the following error:
arcpy.CopyFeatures_management(Temp_Transe_Alleys, DP3LW_Transe_Alleys, "", "", "")
File "C:\Program Files\ArcGIS\Desktop10.0\arcpy\arcpy\management.py", line 1943, in CopyFeatures
raise e
ExecuteError: ERROR 000601: Cannot delete C:\Temp\DestinationFiles.gdb\TRANSE\Transe_Alleys. May be locked by another application.
Since you say this shouldn't happen I'll bring it up with ESRI Support Canada.
Here is the code I have been using on an SDE 9.2.6 Oracle database and it works fine.
# Select all Alleys and set their speed value to 10
gp.Delete_management(DP3LW_Transe_Alleys, "FeatureClass")
gp.Select_analysis(DP3LW_TRANSE_CENTERLINE, DP3LW_Transe_Alleys, "CLASS_CODE = 14")
gp.CalculateField_management(DP3LW_Transe_Alleys, "SPEED", "10", "VB", "")