java - Cannot change configuration ':PayUMoneySDK-Android-master:classpath' after it has been resolved

Question

I am integrating PayU payment gateway and I am get the following error:

"Cannot change configuration ':PayUMoneySDK-Android-master:classpath' after it has been resolved."
"Cannot change configuration ':PayUMoneySDK-Android-master:classpath' after it has been resolved."
"Cannot change configuration ':PayUMoneySDK-Android-master:classpath' after it has been resolved."

I am using Android Studio, latest version.

The following is the build Gradle code:

    apply plugin: 'com.android.library'

    android {
        compileSdkVersion 20
        buildToolsVersion "21.1.2"

        defaultConfig {
            minSdkVersion 14
            targetSdkVersion 20
            versionCode 2
            versionName "1.0"
        }
        buildTypes {
            release {
                minifyEnabled false
                proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'
            }
        }

        buildscript {
            repositories {
                mavenCentral()
            }
            dependencies 
    {

                   classpath 'com.android.tools.build:gradle:1.2.3'
            }
        }
    }

    dependencies {
        compile('de.keyboardsurfer.android.widget:crouton:1.8.+@aar') {
            exclude module: 'support-v7'
            compile 'com.android.support:appcompat-v7:18.0.+'
            classpath 'com.android.tools.build:gradle:1.1.1'
        }
        compile fileTree(include: ['*.jar'], dir: 'libs')
        compile 'de.greenrobot:eventbus:2.2.1'
        compile 'com.loopj.android:android-async-http:1.4.6'
        compile 'com.mobsandgeeks:android-saripaar:1.0.3'
        compile 'com.astuetz:pagerslidingtabstrip:1.0.1'
        compile project(':CustomBrowser-release')
    }

The error is showing in "classpath 'com.android.tools.build:gradle:1.2.3'"..

The below dependencies are PayU dependencies