Hellou.
I'm programmer and front-end developer with years of experience specialised in osCommerce stores.
I've been working as technician on osc helpdesk. I was also moderator and admin on biggest polish osc forum.
For coupons i can use contribution pointed by you or one of my favirites , depending of what functions do you need.
As for fedex, there can be couple od reasons, starting with courier updates/changes... ending on soft change on server. It may be also minor error.
In most cases it can be fixed pretty fast.
If you wanna do it fast, please pick you developer and lets go :-)
If you need some more intel, im here for you.
All the best,
Trygon eXtreme