log4net: error could not create appender [RollingLogFileAppender]

Question

So, I have a project in git repo, and 2 branches: master and fix-master. I've not changed code associated with log4net in fix-master. But every time, when I've started master - I don't have this problem, if I checkout to fix-master, I have this error after this line:

private static readonly ILog Log = LogManager.GetLogger(typeof(Program));

Answer 1

Aside from the obvious candidates (illegal filepath, permissions error), the problem could even be mutex locking:

https://issues.apache.org/jira/browse/LOG4NET-506

RollingFileAppender locking log folder in some cases

Abstract:
In some configuration cases, the rolling file appender may issue a mutex lock on the folder name. If more than one processes try to do that with different executing identity, only one will be able to log to its specific logs file. The others will no more be able to do it.

SUGGESTION:

Add this line to your app.config/web.config, under appSettings, to enable internal debugging:

<add key="log4net.Internal.Debug" value="true"/>

This will give you output like this, to both the system console and to System.Diagnostics.Trace

log4net:ERROR Could not create Appender [RollingLogFileAppender] of type [log4net.Appender.RollingFileAppender]. Reported error follows.
System.UnauthorizedAccessException: Access to path 'D__Logs_' denied. (Translated from french)
   à System.IO.__Error.WinIOError(Int32 errorCode, String maybeFullPath)
   à System.Threading.Mutex.MutexTryCodeHelper.MutexTryCode(Object userData)
   à System.Runtime.CompilerServices.RuntimeHelpers.ExecuteCodeWithGuaranteedCleanup(TryCode code, CleanupCode backoutCode, Object userData)
   à  System.Threading.Mutex.CreateMutexWithGuaranteedCleanup(Boolean initiallyOwned, String name, Boolean& createdNew, SECURITY_ATTRIBUTES secAttrs)
   à  System.Threading.Mutex..ctor(Boolean initiallyOwned, String name, Boolean& createdNew, MutexSecurity mutexSecurity)
   à  System.Threading.Mutex..ctor(Boolean initiallyOwned, String name, Boolean& createdNew)
   à  log4net.Appender.RollingFileAppender.ActivateOptions()
   à  log4net.Repository.Hierarchy.XmlHierarchyConfigurator.ParseAppender(XmlElement appenderElement)
log4net:ERROR Appender named [RollingLogFileAppender] not found.

Please try this, and post back what you find!