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No one knows but Apple. But as it's a beta, there are likely to be protocol changes that make newer builds incompatible with older builds. After release, I would not expect them to make changes to the protocol that break compatibility.
 
Does anyone have an answer?

The obvious answer is that they have changed how iMessage works in the newer beta release and that as such it is incompatible with the original release.

It would not be surprising if future beta (and final) releases of iOS 5 are incompatible with the current beta build's iMessage.
 
They probably changed the protocol as other posters said. It's a beta so is to be expected. You have to upgrade your beta anyway or the beta would expire and be unusable.
 
Like others have said, iMessage protocols and code probably changed. Also, Apple may have changed something on its servers making it incompatible with beta 1.
 
... well yes, these are the obvious answers. The quesiton is, what exactly has changed?
 
... well yes, these are the obvious answers. The quesiton is, what exactly has changed?

Put simply, only Apple knows - there is no reason why Apple would disclose information like that.

I also doubt that anyone would try and reverse engineer the software to work it out, it's simply not worth the effort.
 
... well yes, these are the obvious answers. The quesiton is, what exactly has changed?

Nobody outside of Apple is every going to know the exact reason.

Why does it even matter? Whoever you're trying to message on iMessage is going to have to update to beta 2 anyways because beta 1 will expire eventually.
 
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