We need more info on the exhaust. Is it a full exhaust with Dinan x-pipe or just a Dinan rear section. The tune may have turned off the rear O2 sensors to avoid a CEL for missing cats. This will come up as "not ready" causing you to fail.
2008 IB E92 M3| BBS | KW | Arkym | Platte Forme A.G. | Active Autowerke | K&N | Fabspeed | Dinan | Evolve-R