Lane capacity too small

In a Debug mode run, the solution ships more on this lane than its Capacity allows, by the amount shown. The lane cannot carry what the network needs through it.

What to do

Raise the Capacity on that lane in the data Map Lanes reads, or add another route around it. If leaving demand unserved is acceptable, turn on Allow partial demand fulfillment in Network Optimization with Maximize Profit or Weighted with Profit Weight above 0. Minimize Emissions and Weighted with Profit Weight 0 refuse partial demand.

Where it comes from

Shown by Network Optimization. It is one of the messages about the scenario.