To answer your question, according to MSDN:
This attribute should never be set to false in a production Web site.
(Of course, the default is also false ...) Which suggests to me that you want to be very careful doing this.
Can you include a link to the resource you found online that suggested you switch this off?
Next, according to an MSDN blog:
The problem is that if a POST back is performed and goes to a different server, you will get a nice little error message saying “Corrupt View State“.
To fix this, you can either set enableViewStateMac to false in the element or specify a common value for the validationKey attribute in the element across all servers (in the farm).
Which suggests to me that, unless the error message has changed (quite possible), this isn't what you're running into.
Take a look at this accepted answer - http://stackoverflow.com/questions/686873/allowing-session-in-a-web-farm-is-stateserver-good-enough/687162#687162 - over on Stack Overflow to make sure you're setup correctly.
MSDN also has an article ASP.NET Session State Overview that discusses setting up session state.
At this point, I think it's a configuration issue. Changing machine.config should have restarted the app pools, so that's probably not the issue.