Hello Arun,
I don' know whether it's a typing mistake, but changing your configuration to one as shown below should take care of the problem.
<configuration>
<configSections>
<section name="log4net" type="log4net.Config.Log4NetConfigurationSectionHandler" />
</configSections>
<log4net>
<appender name="FileAppender" type="log4net.Appender.FileAppender">
<file value="D:\\TestProj\\TestLog.txt" />
<appendtofile value="true" />
<lockingmodel type="log4net.Appender.FileAppender+MinimalLock" />
<layout type="log4net.Layout.PatternLayout">
<conversionpattern value="%date [%thread] %level %logger - %message%newline" />
</layout>
<filter type="log4net.Filter.LevelRangeFilter">
<levelmin value="INFO" />
<levelmax value="FATAL" />
</filter>
</appender>
<root>
<level value="DEBUG" />
<appender-ref ref="FileAppender" />
</root>
</log4net>
</configuration>
Regards,