That worked for me as well with the column as character.
There actually is another level of complexity since the original file is an html file that is saved in excel with an html extension (automated data from a machine). So I do the following:
FileList = pick file("Select Data");
//Rename xls to html
Basefile=Substr( FileList, Contains( FileList, "/", -1 )+1 );
basefile2=left(Basefile,length(Basefile)-3);
Copy File(FileList,basefile2||"html");
FileList_final = basefile2||"html";
That is done before I do the previous open function (here again for reference):
dtcd = Open(
FileList_final,
"invisible",
HTML Table( 1, Column Names( 0 ), Data Starts( 1 ) ),
);