SPA3000 dial plan issue

I am trying to configure a SPA3000 to send the vertical service activation codes to the PSTN. I first removed all the vertical service codes from the SPA configuration as is suggested on the Linksys tutorial. This is my dial plan.

(*xx<:@gw0>|x11S0<:@gw0>|10n|2nn|xxxxxxx.<:@gw0>)

The SPA seems to ignore the *xx<:@gw0> Upon dialing a *xx code the SPA gives an immediate fast busy. The rest of the dial plan works fine. If I replace *xx<:@gw0> with *xx the * codes route correctly to trixbox. If I replace *xx<:@gw0> with, for example 7xx<:@gw0> the 7xx number is routed correctly to the PSTN. Somehow the *xx gets the SPA confused. I am baffled by this problem.