Welcome to SW forums Dave.
What is you SW version and SP. How you're opening/importing the files in SW. While in open file dialog box, after you set the file type to ACIS and then click on options on the RH corner, you'll see some options for importing file. Try to adjust them and check. OR if you can upload the file here, someone might do it for you.
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Like Deepak mentions click on the "options" button in the SW open file dialog box. Sounds like the file's units need to be changed in that it is trying to import something that is too small.