I set "x_test_request" to FALSE and waited a couple days to make sure my authorize.net account is setup, but I'm still getting the same error.
I did set the cart up for AIM processing rather than SecureSource, primarily because I couldn't find any information at all about either of these from both the webassist site and the authorize.net site. I don't know if this would have any relation to the error I'm getting..
Has anybody else here encountered this error with auth.net before? In the mean time, I'm also contacting auth.net to see if they have some input on this.