Do you have features outside the spatial extent?
Can you provide more information on where the current geometric network is located?
It is hard to know much with out some more details, is the output a local file geodatabase or on a network share?
The feature dataset that contains the geometric network (sanitary sewer)was copied to a file gdb on a network share. I had no issues when converting another one (storm water). I have tried putting the second one into its own file gdb.but get the same error each time I run the convert tool.