Upload File Error in HttpUnit

El file es readable y lo accedo en el test via inputStream.read() pero en la llamada desde httpunit
escupe la exception:
java.io.IOException: Read error
at java.io.FileInputStream.readBytes(Native Method)
at java.io.FileInputStream.read(FileInputStream.java:194)
at com.meterware.httpunit.MimeEncodedMessageBody$MimeEncoding.addFile(MimeEncodedMessageBody.java:145)
at com.meterware.httpunit.FileSubmitFormControl.addValues(FormControl.java:944)
at com.meterware.httpunit.WebForm.recordParameters(WebForm.java:584)