If the initial transaction from outside the banking system is dictated by the errant accounting system of a non-compliant enterprise, it must be cordoned off and somehow redressed manually. Such malfunctions occur all the time, but at Y2K they are more likely to come in waves that may overwhelm manpower. Supply chain disruptions grow to chronic levels. There are serious problems in government services, including delays in distribution of welfare and Medicaid checks. The U.S., Europe and Japan have negative GDP growth in the first quarter and zero or negative growth in the second quarter.
Most global economies go into recession.
Air and sea traffic would be halted in many places. Nuclear plant malfunctions would be possible. In the U.S. and Europe, government aid programs would experience high failure rates soon after rollover. Banking and finance industry problems are systemic, causing substantive problems in the international settlements mechanism. Certain areas of the world are unable to restore basic industrial functions for the following month.