Seth Call reports:

http://www.qos.ch/pipermail/slf4j-user/2010-February/000889.html

It appears that but not certain that a logback appender is invoking a library
using log4j during its initialization which retrieves a NOPLogger.

See

http://www.qos.ch/pipermail/slf4j-user/2010-February/000892.html

Solution is to change the Category.log(String FQCN, Priority p, Object msg, Throwable t) method from

public void log(String FQCN, Priority p, Object msg, Throwable t)

{ int levelInt = priorityToLevelInt(p); differentiatedLog(null, FQCN, levelInt, msg, t); }

public void log(String FQCN, Priority p, Object msg, Throwable t) {
int levelInt = priorityToLevelInt(p);
if (locationAwareLogger != null)

{ locationAwareLogger.log(null, FQCN, levelInt, convertToString(msg), t); }

else

{ throw new UnsupportedOperationException("The logger [" + slf4jLogger + "] does not seem to be location aware."); }

}