Recently, I had also received the same validation error in ArcMap 10.2.
The problem was with my Fittings feature class participating in geometric network.
1. Repair Geometry will Not solve the problem.
2. I deleted the geometric network.
3. Rename the existing Feature Class with validation error like "Fittings_1".
4. Export "Fittings_1" feature class to new feature class with the same name like "Fittings" and in the same feature data set.
5. Check Validation on some features of new "Fittings" feature class in ArcMap without creating Geometric Network.
6. When OK. Recreate Geometric Network.
7. Check Validation again on some features of new "Fittings" feature class.
8. Define Connectivity Rules and Weights, if required.