With some browsers, sometimes, I may have this error:

"Unable to validate data."

This comes from this stack trace:

at System.Web.Configuration.MachineKeySection.GetDecodedData(Byte[] buf, Byte[] modifier, Int32 start, Int32 length, Int32& dataLength)
   at System.Web.UI.ObjectStateFormatter.Deserialize(String inputString)

On another application, this was only happening when the page was configured with allow an update among data entry fields. So, I added:

EnabledEventValidation=false

to take care of that. This was happening with IE 6.0. Since then, I never add that problem on that page. But, on another application, which is a Default.aspx page, where there is no control to allow an upload, I had this error tonight. The browser was:

Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.8.1.14) Gecko/20080404 Firefox/2.0.0.14

So, to avoid errors with non IE 7.0 browsers, does this mean I have to put EnabledEventValidation=false on all .aspx pages?