logback.xml文件中不支持的类型'property'

我想在Android项目中使用logback-android。这是我所做的

我已将jar文件复制到libs文件夹中

• logback-android-1.1.1-2.jar
• slf4j-api-1.7.6.jar

并在资产文件夹中有logback.xml

<configuration debug="true">
    <property name="LOG_DIR" value="/mnt/sdcard/com.sf.quid/logs" />

    <!-- Create a logcat appender -->
    <appender name="LOG_CAT" class="ch.qos.logback.classic.android.LogcatAppender">
        <encoder>
            <pattern>%msg</pattern>
        </encoder>
    </appender>

    <!-- Rolling Appender -->
    <appender name="FILE" class="ch.qos.logback.core.rolling.RollingFileAppender">
        <!-- File location -->
        <file>${LOG_DIR}/quidpos.log</file>

        <!-- Only log error messages to log file --> 
        <filter class="ch.qos.logback.classic.filter.LevelFilter">
            <level>DEBUG</level>
            <onMatch>ACCEPT</onMatch>
            <onMismatch>DENY</onMismatch>
        </filter>

        <!-- Rolling Policy -->     
        <rollingPolicy class="ch.qos.logback.core.rolling.FixedWindowRollingPolicy">
            <fileNamePattern>${LOG_DIR}/quidpos.%i.log</fileNamePattern>
            <minIndex>1</minIndex>
            <maxIndex>1</maxIndex>
        </rollingPolicy>

        <triggeringPolicy class="ch.qos.logback.core.rolling.SizeBasedTriggeringPolicy">
            <maxFileSize>1MB</maxFileSize>
        </triggeringPolicy>

        <!-- Message encoder -->
        <encoder>
            <pattern>%d{HH:mm:ss.SSS} [%thread] %-5level %logger{35} - %msg%n</pattern>
        </encoder>
    </appender>

    <!-- Log level - change this to ERROR on release -->
    <root level="debug">
        <appender-ref ref="LOG_CAT"/>
        <appender-ref ref="FILE" />
    </root>
</configuration>

这是build.gradle文件中的依赖项部分

dependencies {
    compile 'com.android.support:support-v4:19.+'
    compile fileTree(dir: 'libs', include: ['*.jar'])
}

我正在使用Android Studio 0.6.1和Gradle 1.12（Android插件0.11。+），当我尝试Clean项目，Run等选项时，它导致以下错误

Error:Execution failed for task ':multipos:mergeDebugResources'.
Unsupported type 'property' in file C:\Users\Jagmohan\AndroidStudioProjects\MultiPOS\multipos\src\main\res\assets\logback.xml

如果有人可以识别出潜在的问题，请回答。

谢谢！