A block too large for older software splits the network in two. Developers and miners coordinate to rejoin it within hours.
A block that had a larger number of total transaction inputs than previously seen was mined and broadcasted. Bitcoin 0.8 nodes were able to handle this, but some pre-0.8 Bitcoin nodes rejected it, causing an unexpected fork of the blockchain.
BIP 50 · What went wrong
SATOSHI ON SCALABILITY
The design outlines a lightweight client that does not need the full block chain. In the design PDF it's called Simplified Payment Verification. The lightweight client can send and receive transactions, it just c…