Paul,
I think I've discovered that the cause of the problem is not the precision of the data, but the format of the end of line characters. My file had Mac end of line characters; I assume yours was in Windows format.
I tried rounding the data to four places within Excel for Mac, saving as tab delimited .txt, and I get a file that shows no visible differences when compared with the one you uploaded here (FSR_load_BOS_rounded.txt). It gives me the same error, however, whereas yours does not.
I then used a freeware converter to convert the EOL characters in my file to windows format. The resulting file imported with no errors. I then discovered that Excel includes options to save as Windows .csv or Windows .txt, and those work fine as well.
Finally, I imported the data without rounding but in Windows .txt format, and it worked fine, displaying in the edit window the numbers rounded to 4 decimal places.
So perhaps the fix to SAM is to allow it to import text (or csv) files with EOL characters in Mac format. In the meantime, you could include a note in the documentation mentioning the limitation.
Thanks.