I know that the emotion chip in Data became fused apparently because of some information overload, but doesn't that seem to be a bit of a cop-out? In such an advanced android, as I'm sure we would all agree, surely there would have been some safety devices installed in Data against fusing. The emotion chip was made specifically by Dr Soong for Data, so I'm at a loss as to why Data's emotion chip became fused in Generations. The only thing I can think of is that Soong had some intention for the chip to fuse (funnily enough though, it didn't fuse in Lore...)
In the absence of an on-screen explanation… the chip had kind of been through a bit.
It was designed for Data as Soong revealed in the episodes 'Brothers', but instead it was Lore who ended up using it -- presumably, in tandem with his own, though that's a tad nebulous.
At any rate, the chip was running around in the wrong android for a few years, before Data retrieves it at the end of 'Descent, Part II'. Data later notes the chip was damaged during the exchange, so in concert with running around in the wrong Soong-type for a few years... sounds to me like conditions were ripe for a bad wire or two.