What Conditions would make the Numeric Overflow Message to Appear during a New MRP Run?

This message appears because somewhere you have a date or date-related field, or a conversion field that is causing a number to be out of range for the size allotted for the answer. 
Three possible causes are:
  1. Production Calendar is not configured correctly
  2. SO, WO dates are incorrect
  3. An assembly contains itself as a subassembly.
Examples might be if if you have entered a due date somewhere for 06/21/2070 instead of 06/21/2007, or entered a leadtime of 38 months instead of 38 days.  Or, possibly a conversion factor for purchasing that resulted in a number too big for the system.
 
MRP will still run okay, and the user can usually find the error by looking at the dates on the action messages - they will be at one end or the other if their production calendar.  If it is a quantity problem, the number will simply show as ****, indicating an over flow number.