You are sharing a utility network, or a layer that is used in a utility network, as a feature layer that references registered data. You did not select the Only allow true curve updates by true curve clients option. When you share utility network datasets as feature layers, this setting is required.
Solution
Choose only to allow true curve updates by true curve clients.
Hover over the analyzer message. Click the Options button
that appears and click Show Feature Properties. In the Share As Web Layer pane, on the Configuration tab 
, check the Only allow true curve updates by true curve clients box. This requires that the Allow geometry updates and Allow update of true curves options are enabled.
More information
Editing true curves through a client that does not support true curves creates densified lines that are not supported by a utility network. To ensure that true curves are maintained, only clients that support true curves are allowed to edit geometries that have true curves.