Yeah, that's usually the next error I get too
. I take it, then, that you have this array in mdadm.conf? Anyway, comment out the array in mdadm.conf before restarting; stopping the array just idles it (which is ordinarily a good thing). I seem to remember having to use --zero-superblock for this once but I don't recall if that was before I loaded up the drives with data.
I *just* had this happen last week and I'm looking through my logs, but I'm not finding any magic fix. The only difference is I don't have my array in mdadm.conf; I start it manually to see if anything's gone wrong, so when I restart the machine the array isn't assembled. Again, however, mine's on a separate box so it's rarely restarted.
On another note, with 2 spares you might want to consider RAID 6 instead of 5; tolerates the loss of 2 drives and as we know, the higher the number of drives in an array the more likely a multiple failure will occur.