I have no clue; why you get an error, but something is indexing into an illegal location in some sort of collection. There could be some misunderstandings related to intermixing of testnet and mainnet addressing. IMO; it's likely causing trouble.
Are you preparing the homestead explorer?
I am a bit reluctant to trust the new code, unless we can 100% exclude the possibility that it might be creating transactions or p2p communications that crashed my node - which had been running fine for almost a year,
until block 1820081.
Fair enough. It might be that the new code interfere old client communication.
I think, if all would upgrade to the new client, problems would disappear.
I think the best is to play with the testnet for the moment - if doubts are gone - we can all upgrade to the new gsoil in the future if you want.