You might also try getting rid of most, if not all, of the empty columns. I'm not sure, but a limit on the number of fields. In any case, they just bloat the file. Also, as well as no spaces in the column names, maybe Excel column names need to be under 13 characters like a dbf. It doesn't hurt, anyway. If you wanted to make a shapefile out of the data, you'd need to do it then.