>>I'm not sure how the EnableEventValidation setting would have any effect on a 'Invalid viewstate' error.
>>
>>Setting EnableViewState to false would certainly stop to error since there would be no ViewState to validate <s>. But whilst you may not need to maintain ViewState on this particular page I assume there are other pages where this is not so - and those pages are probably still prone to the invalid viewstate error.
>>
>>I'd suggest implementing the fixed key as recommended in the link Tracy supplied.
>
>Since I have this in the Pages declaration of the Web.config file, I didn't get that message again.
>
>

>enableEventValidation="false"
>

>
>I had those errors at a few occasions for two days until I added that parameter. Now, for two days, I didn't get it. I will keep an eye on this however as it might just be a coincidence.

Hi,
Can you confirm that with EnableViewState=false and EnableEventValidation= true you were actually getting the "Invalid ViewState" rather than the "Invalid CallBack" error?

FWIW I read that doing things like adding options to DropDownLists in client code can trigger the "Invalid Callback" exception.....

Regards,
Viv