If you are planning to move from 1.2.10.0 to log4net 2.0.x+:
When a project uses a modern log4net version but a dependency requires 1.2.10.0, the runtime fails because the PublicKeyTokens do not match (1.2.10.0 uses 1b44e1d426115821 , while later versions use 669e0ddf0bb1aa2a ). log4net 1.2.10.0
Allows for granular control by selectively enabling log statements at different levels (DEBUG, INFO, WARN, ERROR, FATAL). If you are planning to move from 1