AppleScript choose file dialog box with default location not working
Both scripts don't work for me. The problem is that the default location parameter needs to be of type alias. You can fix it by adding POSIX file in front of your path (the path does need to exist, otherwise you also get an error message):

set strPath to POSIX file "/Users/lowken/Dropbox/"

choose file with prompt "Please choose a file:" of type {"XLSX", "APPL"} ¬
    default location strPath


Or you could use the "old style" HFS format:

set strPath to alias "Macintosh HD:Users:lowken:Dropbox"

choose file with prompt "Please choose a file:" of type {"XLSX", "APPL"} ¬
    default location strPath