Invalid Viewstate, Invalid length for a Base-64 char array or string

Question

I face this error from time to time,

ExecuteStep at line:0 at Column:0 The state information is invalid for this page and might be corrupted. (*)Invalid viewstate

Inner exception:

unhandled exception in Application_Error At Load at line:0 at Column:0 Invalid length for a Base-64 char array or string

debugging is enabled, and the pdb file exists, and as you see the debug info does not exactly tell me where it happened.

I'm using ASP.NET, C#, DotNet 4.5

this only occurs on a specific page's load.

[FormatException: Invalid length for a Base-64 char array or string.]
   System.Convert.FromBase64_Decode(Char* startInputPtr, Int32 inputLength, Byte* startDestPtr, Int32 destLength) +10545359
   System.Convert.FromBase64CharPtr(Char* inputPtr, Int32 inputLength) +130
   System.Convert.FromBase64String(String s) +41
   System.Web.UI.ObjectStateFormatter.Deserialize(String inputString, Purpose purpose) +66
   System.Web.UI.ObjectStateFormatter.System.Web.UI.IStateFormatter2.Deserialize(String serializedState, Purpose purpose) +8
   System.Web.UI.Util.DeserializeWithAssert(IStateFormatter2 formatter, String serializedState, Purpose purpose) +40
   System.Web.UI.HiddenFieldPageStatePersister.Load() +127

[ViewStateException: Invalid viewstate. 
    Client IP: ::1
    Port: 
    Referer: http://localhost:8000/ERP/MemberArea/Permits/Process_New.aspx
    Path: /ERP/MemberArea/Permits/Process_New.aspx
    User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; Trident/7.0; rv:11.0) like Gecko
    ViewState: 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...]

[HttpException (0x80004005): The state information is invalid for this page and might be corrupted.]
   System.Web.UI.ViewStateException.ThrowError(Exception inner, String persistedState, String errorPageMessage, Boolean macValidationError) +198
   System.Web.UI.HiddenFieldPageStatePersister.Load() +266
   System.Web.UI.Page.LoadPageStateFromPersistenceMedium() +88
   System.Web.UI.Page.LoadAllState() +36
   System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint) +6704
   System.Web.UI.Page.ProcessRequest(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint) +245
   System.Web.UI.Page.ProcessRequest() +72
   System.Web.UI.Page.ProcessRequestWithNoAssert(HttpContext context) +21
   System.Web.UI.Page.ProcessRequest(HttpContext context) +58
   ASP.memberarea_permits_process_new_aspx.ProcessRequest(HttpContext context) in c:\Windows\Microsoft.NET\Framework\v4.0.30319\Temporary ASP.NET Files\ERP\5da93c6f\27d5fbc5\App_Web_llo4zgw1.4.cs:0
   System.Web.CallHandlerExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute() +341
   System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean& completedSynchronously) +69

Answer 1

All credits go to @Aristos for providing his answer on another question: Click here

he provided three possibilities, my problem was that the page was reloading tripple times causing the viewstate to get corrupted.

I have a customized JQuery datepicker, and there was a javascript code to call an OnvalueChanged event, I was comparing two date values which were the same but had a different format, which caused the event to fire more than once somehow.

to debug this, put a breakpoint on the Page_Load event, and if it gets fired more than once, then start to remove some code/usercontrols, scripts until you catch the cause.