Android Question RDC problem

i'm a b4a beginners and i'm trying to make an android application that connect to mysql database.
when i compile/debug, i got this error :

B4A version: 6.00
Parsing code. (0.01s)
Compiling code. (0.29s)
Compiling layouts code. (0.01s)
Organizing libraries. (0.00s)
Generating R file. (3.29s)
Compiling debugger engine code. (3.93s)
Compiling generated Java code. (3.92s)
Convert byte code - optimized dex. Error
UNEXPECTED TOP-LEVEL EXCEPTION:
java.lang.IllegalArgumentException: already added: Lanywheresoftware/b4a/samples/httputils2/httpjob;
at com.android.dx.dex.file.ClassDefsSection.add(ClassDefsSection.java:122)
at com.android.dx.dex.file.DexFile.add(DexFile.java:161)
at com.android.dx.command.dexer.Main.processClass(Main.java:615)
at com.android.dx.command.dexer.Main.processFileBytes(Main.java:570)
at com.android.dx.command.dexer.Main.access$2(Main.java:546)
at com.android.dx.command.dexer.Main$2.processFileBytes(Main.java:514)
at com.android.dx.cf.direct.ClassPathOpener.processArchive(ClassPathOpener.java:284)
at com.android.dx.cf.direct.ClassPathOpener.processOne(ClassPathOpener.java:166)
at com.android.dx.cf.direct.ClassPathOpener.process(ClassPathOpener.java:144)
at com.android.dx.command.dexer.Main.processOne(Main.java:537)
at com.android.dx.command.dexer.Main.processAllFiles(Main.java:449)
at com.android.dx.command.dexer.Main.runMonoDex(Main.java:236)
at com.android.dx.command.dexer.Main.run(Main.java:206)
at com.android.dx.command.dexer.Main.main(Main.java:179)
at com.android.dx.command.Main.main(Main.java:103)
1 error; aborting

i can't figure out what's wrong.. please help. thank you