Well you did something you should never do, that is disconnect a HD that had not failed after already having a failed drive that had not completed the resync. Normally when this happens you must use a recovery service to recover your data.
You also have a larger HD in drive 1 position. This is a
NO NO on snaps.
They use this drive to determine the size af the raid5 array. All starting blocks must be the same.
Having 2 drives failed on a 4 drive raid5 you do not have enough parity data on 2 drives to recover from. This applys to ALL RAID5 units. Your only choice is a recovery service.
You would have been a lot better off by pulling the cat5 cable from the 4100 dropping off all users. Then give the snap time to do the resysnc. Then connect using a crossover cable if the snap has a static IP. Or use a managed switch to kick the users off by creating a virtual lan, with the 4100, your pc and backup server/drive. At times it takes a snap several hrs to come on line. This happens when it is doing a check/resync on the drives.
Also check to make sure your units has been repaired to handle larger drives. Sticky on top of thread. Not all 4100 were repaired. Snap only contacted 4100 240gig owners that had registered with them. So units upgraded were not repaired.
Sorry being the bearer of BAD NEWS.
Being impacient (panic) caused you to destroy the raind5 array.
My recommendation right now is for you to contact a recovery service. You should have 3 drives that contain all of your data. Your original failed HD may not be complete. This will be expensive, but if you must have the data, it's your best chance. Under NO Circumstances move your drives to a PC and try to read the drives. The file structure is a Highly Modified XFS on BSD, so nothing but a snap or special recovery software can read the drives.