GXDLMSTranslator

Hello! I have tried to realize message translation to xml as it makes GXDLMSDirector. There is my code, i took one message just to try it:
buff = GXByteBuffer()
buff.setHexString('7EA00703619369477E')
t = GXDLMSTranslator()
xml = t.dataToXml(buff)
But it throws me a mistake - ValueError: Invalid data type. Then I passed this message to translator in GXDLMSDirector, and it worked, application gave a responce:
1: 7E A0 07 03 61 93 69 47 7E
<HDLC len="9" >
<TargetAddress Value="1" />
<SourceAddress Value="30" />
<!-- SNRM frame. -->
<FrameType Value="93" />
<Snrm>
</Snrm>
</HDLC>
What did I do wrong in my code that it threw an exception?