"Invalid Character in Base-64 String" using ASP.NET and C#

Question

I'm having this problem on posting a page. The page have a jquery ajax load called by the onchange of a dropdownlist, if I disable the onchange, the post works.

"The state information is invalid for this page and might be corrupted"

[FormatException: Invalid character in a Base-64 string.]
   System.Convert.FromBase64String(String s) +0
   System.Web.UI.ObjectStateFormatter.Deserialize(String inputString) +72
   System.Web.UI.ObjectStateFormatter.System.Web.UI.IStateFormatter.Deserialize(String serializedState) +4
   System.Web.UI.Util.DeserializeWithAssert(IStateFormatter formatter, String serializedState) +37
   System.Web.UI.HiddenFieldPageStatePersister.Load() +113

[ViewStateException: invalid Viewstate. 
         Client IP: 127.0.0.1
         Port: 
         User-Agent: Mozilla/4.0 (compatible; MSIE 8.0; Windows NT 5.1; Trident/4.0; .NET CLR 1.1.4322; .NET CLR 2.0.50727; .NET CLR 3.0.4506.2152; .NET CLR 3.5.30729)
         ViewState: 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...]

[HttpException (0x80004005): As informações sobre estado são inválidas para esta página e podem estar corrompidas.]
   System.Web.UI.ViewStateException.ThrowError(Exception inner, String persistedState, String errorPageMessage, Boolean macValidationError) +106
   System.Web.UI.ViewStateException.ThrowViewStateError(Exception inner, String persistedState) +14
   System.Web.UI.HiddenFieldPageStatePersister.Load() +217
   System.Web.UI.Page.LoadPageStateFromPersistenceMedium() +105
   System.Web.UI.Page.LoadAllState() +43
   System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint) +6785
   System.Web.UI.Page.ProcessRequest(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint) +242
   System.Web.UI.Page.ProcessRequest() +80
   System.Web.UI.Page.ProcessRequestWithNoAssert(HttpContext context) +21
   System.Web.UI.Page.ProcessRequest(HttpContext context) +49
   ASP.content_search_default_aspx.ProcessRequest(HttpContext context) in c:\WINDOWS\Microsoft.NET\Framework\v2.0.50727\Temporary ASP.NET Files\web-site-2009\e4bfc9d6\d5d6c855\App_Web_zcb1qfmu.0.cs:0
   System.Web.CallHandlerExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute() +181
   System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean& completedSynchronously) +75

what could be the reason for that? Anyone seen it before?

Thank you

EDIT:

So, I've found out why this is happenning. At the end of Page_Load, I write a javascript line that calls a jquery function that loads new fields into a div. So, as I see, this is causing to create a inconsistence on the viewstate. Disabling ViewState is not a option for this case. It works on FF, and it bugs on IE. Anyone?

Thank you

Answer 1

Here is an explaination of the problem with alternative solutions:

http://blogs.msdn.com/tom/archive/2008/03/14/validation-of-viewstate-mac-failed-error.aspx

Answer 2

Just ran into this. Remove the form tag from the page you are loading via jquery.