Hi m8,
I don't know if this will help you but i've just had stress with secpay. It turns out that secpay doesn't like spaces in the shop name. eg "My Shop" will cause failure but if you change it to "My_Shop" it works!
The only other thing I have is the -jredir option set on the merchant id. You're more than welcome to the module i'm currently using if you need it.
Regards,
Mark.