When Redsn0w 0.9.14b1 was released to downgrade iPhone3G/3Gs running the iPad baseband in order to reactivate GPS functionality, many of you may have had issues with the downgrading process. MuscleNerd released 0.9.14b2 today to fix those issues.
So far I have talked to 5 people who had issues downgrading with b1 and b2 worked for all 5 of them.
Redsn0w 0.9.14b2 - Windows
Redsn0w 0.9.14b2 - Mac
In order to downgrade simply place your device into DFU mode, open Redsn0w, hit jailbreak and then on the options screen uncheck all boxes except for "downgrade ipad baseband" Be sure not to interrupt the process as interrupting a baseband flash could permanently brick your cell radio. The process takes ~5-7 minutes.