Failed to load viewstate

Error:

Failed to load viewstate. The control tree into which viewstate is being loaded must match the control tree that was used to save viewstate during the previous request. For example, when adding controls dynamically, the controls added during a post-back must match the type and position of the controls added during the initial request.

One possibility is that the query that selects the count and the query that selects the fields are in disparity. The count query must return the number of rows that would be returned by an unlimited field query.

The name xxx Does Not Exist in the Current Context

This post helped me to realize that when I made copies as backups of "infringements.aspx" and "infringements.aspx.cs" named "copy of infringements.aspx" etc, the "copy of infringements.aspx" still referenced "infringements.aspx.cs" and caused the compiler some confusion.

Sys$CultureInfo$_getAbbrMonthIndex

Sys.ParameterCountException: Parameter count mismatch.'
function Sys$CultureInfo$_getAbbrMonthIndex(value)

I got this error when I had two controls that used javascript to show a modal popup extender. The control which was named by the mpe as the TargetControlID would not cause this error, but the other control would. (Infringements.aspx/mpeNoticeConfirm)

This appears to be a problem with the Web Developer 1.1.6 plugin for firefox. On computers without that plugin, the error console does not display the error.