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Which version of SW are you running. If SW 2007 SP2.2 or prior, I recommend upgrading to SW 2007 SP4 (not SP5) or SW 2008 SP4. There was a bug in older versions from 2006 that bloated files sizes. If this isn't the issue for your, then maybe try using EcoSqueeze on that one file to see if the size drastically reduces.