When I go to Tools->Import, and select the .XML file in question, I get the following error:
Sorry, there has been an error.
This does not appear to be a WXR file, missing/invalid WXR version number.
Here is an answer i found ,though it doesn't work for me ,it truely help some people ,so i paste it for you :
【If you paste the following line into your export file after the Language defining line in the <channel> section near the topyou should be good to go:<wp:wxr_version>1.1</wp:wxr_version>
You may be able to put it elsewhere, but that's where it appeared in my new export and where it worked for me.】
reference :http://wordpress.org/support/topic/xml-to-wxr-issue