I'm not familiar with Credo mobile. Are you trying to tether via WiFi, Bluetooth or USB? With the latest Sprint firmware, it's probably not possible to tether via WiFi unless you pay Sprint or root your phone (and I know nothing about rooting for Credo).
Are you rooted? If so, see the thread in this forum about WiFi tether. Otherwise, there are a bunch of USB tethering apps in the Play store, many of which are free. Give them a try. And since you paid for PDANet, you might want to reach out to their customer support, too.