Proguard say input jar file is specified twice

I create app with Google Translator. I try create signed apk with Proguard. proguard.cfg contain: ``` -libraryjars libs/gtranslateapi-1.0.jar -keep class com.gtranslate.** { *; } ``` proguard-project.txt contain: ``` -dontwarn com.gtranslate.** ``` Also I try without proguard-project.txt: ``` # -dontwarn com.gtranslate.** ``` But I get error: ``` Proguard returned with error code 1. See console Error: The same input jar [C:\workspace\myproject\libs\gtranslateapi-1.0.jar] is specified twice. ``` What is incorrect?