Cannot open cdr file

I created a file in Corel Draw 13 on my computer and sent the design to my sister who also has Corel Draw 13. She cannot open the file and gets a message that the file "is not importable using the selected filters or this format is not supported." We can't figure out what is different between her program and mine. She is on Vista and I am using Windows XP, but this seems more to be a problem with the Corel Draw X3 program. Any suggestions on what to do to open the file?

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