Invalid postback or callback argument.

[Tim Bailey]

Hi all,

I am having a problem with thie "Invalid postback or callback argument."
error, I (or any other developer at the company) has never seen it, but it
our biggest bug. After doing some searching and general messing about I
found that if I run a slowdown proxy (NetLimiter or similar) and simulate a
dialup connection, I can make the error happen. It seems to be when you
have a master page with some controls at the top, the page is loading
slowly, the top controls are visible (login stuff) the user then enters
their details before the rest of the page is complete and submits it. This
means that the __EventValidation form field is not present and the exception
occurs.

Any ideas on how to prevent this in this situation (our biggest error), I am
reluctant to turn it off but I may have to...

TIA

Tim