Need Help Epub To MOBI

Hi,
I have Epub file with Social DRM on it.
I am trying to convart the file to mobi with Kindle Previewer, but I get this massage:

************************************************** ***********
Amazon kindlegen(Windows) V2.9 build 0731-890adc2
A command line e-book compiler
Copyright Amazon.com and its Affiliates 2013
************************************************** ***********

Info:I9026:option: (hidden) amazon creator tool or pipeline

Info:I9014:option: -verbose: Verbose output

Info(prcgen):I1048: Unpacking ePub file

Error(xmlmake):E27012: Item or process id already used: css



Any one Can help PLS?

THX
N.