free shipping causes strange problems! HELP!!!!

HI. i am running 1,3.9h zen-cart. i have free shipping option enabled for continental usa. some customers don't see that option and click on UPS ground shipping. when they do it and process with checkout, in admin panel in some cases (but not in all cases!!!!) i see there is no name and last name being attached to their invoice. the problem is, when i try to refund their shipping, authorize.net refuses to do it. so i need to fix the problem in its root. please tell me what to do so their names show up in invoices. i can not find the logic of this problem, because its not happening with every customer, just with some of them. They are in different USA zones, and they spend different amounts. any help is appreciated. thanks.

What are your settings on the Free Shipping Options freeoptions shipping module?

Check your Zone Definition for the USA Zone that you made and see what the DEFINITIONS are for it ...

I am using the addon for 48 Lower states + DC, i went trough it and looked to every one of them. each has its definitions. The problem is there can be like 5 customers from same state and 4 of them will be fine, and one will have that issue (will be charged for shipping, and will not have name last name in invoice). On Free shipping options i have:
Enable free options true,
Shipping cost 0
Handling fee 0
Total >= 0
Total <= (left blank)
Weight >= 0
Weight <= (left blank)
Item Count >=0
Item Count <= (left blank)
Tax Class none
Tax basis Shipping
Shipping Zone 48 Lower States
Sort Order 0

Also is there a way not to show the UPS shipping rates or an ability to select it at all, in a zone where Free shipping option applies?

Try eliminating issues and use just one setting:

Total >= 0
Total <= (left blank)
Weight >= 0
Weight <= (left blank)
Item Count >=0
Item Count <= (left blank)

Set each to blank except for the:
Total >= 0

and see if that changes things ...

Are you able to reproduce this issue with a particular Product or a particular shipping address?

i did recreate the same order using same address as one of customers with that issue, nothing wrong went wrong with mine...i can see the Free shipping option. they say they don't.

I cannot reproduce the issue ... so I really cannot tell you what the problem might be ...

Have you an URL to your site and the products_id that were added to their order ... plus the ship from would help ... we do not need the street address just the City State Country and Zip Code that they used ...