Hello
Exception messages are very important to keep the planner informed of possible issues during the MRP run.
Exception message 10 is triggered during the rescheduling check and it means that the replenishment proposal should be rescheduled to met the requirement date. Take a look on the following WIKI, which explains the rescheduling process in more details:
http://wiki.scn.sap.com/wiki/display/ERPMan/What+is+rescheduling+and+how+does+it+work
BR
Caetano