just started getting the "validation of viewstate mac" error

I have had a site up and running for quite a while, but I've just started getting the MAC failed error. Quite often too. While coding tonight I've noticed it 4 times or so. The host (through someone else) changed servers and we've had a bunch of issues. Th开发者_如何转开发is started happening since then. What are all the possibilities that it could be on the server end that I could ask? (I don't know all that much about IIS).

Thanks!

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Yes the host has changed something.

All posts are signed with the MAC key. In a load balanced solution the servers need to share the key or the MAC validation fails.

Especially if the servers are load balanced and don't share the MAC key.