Simple question about ordering a table

[Jehannum]

Hello,

I'm writing a dictionary. It's in the form of a 2-column table, with the word in column 1 and the definition in column 2.

I want to order the table alphabetically, based on column 1. Obviously, I want the definitions in column 2 to follow the associated word when the table is sorted.

The words are alphanumeric, and I would prefer that numeric values e.g. "1st family gas" appear at the start, before letter A.

I am having trouble at the moment. When I select column 1 and try Table Tools | Layout | Sort, I get the error message "This entry is not valid for sorting. Please type or select another entry from the list". I do not understand this error message.

Any help would be appreciated.