According to this page: http://shopsite.com/help/current/en-US/sc/pro/index.htm?page=/help/current/en-US/sc/pro/advanced.ordering.options.html if you put ;n at the end of the item (Select Product;n) it is supposed to force the user to make a selection. It is not working on the site I am developing with Manager. Why?
The ;n only prevents people from checking out without making an menu choice. They can still add the item to the cart but will be unable to completely checkout.
There is no built in way to force the text field to be filled in. You might be able to craft some javascript that would check the selected option and if it is one that requires text to be entered not let the shopper check out. There is sample code in forum post for checking some shopping cart parameters but I don't remember anything specific to the text field. Do a search in the forum and see if you can see something that might work for you. Or you could contact some of the 3rd party developers to see if they have anything or could create something for you. See http://www.shopsite.com/developer.html or possibly a certified designer could help http://www.shopsite.com/csd.html.
The "You didn't make a selection" type message is only showing up if one updates the checkout page. I can see that can be a problem if they placed a number of such items in the cart. It's not clear which one. I was looking for a check before proceeding type of thing.
What version of ShopSite are you using? In my ShopSite Pro 11sp2r4 any options that are not selected are highlighted in red when I try to checkout without making a selection.
Even in a Manager store if it is running ShopSite 11sp2r4 it will have the required fields shaded with a light red if the shopper tries to checkout without making a selection.
You can find the version of ShopSite that your store is using by clicking on the ShopSite above the nav bar in the backoffice and then looking in the footer of the page for something like "ShopSite® Manager 11 sp2 r4.3, StoreID: sp2man". If it doesn't say 11 sp2 r4.x you should have your store upgraded to that version.