There are various causes for this error, this is one we had some time ago when paginating through a DataGrid (for this case we’re talking about ASP.NET 1.1); the error appeared systematically under a specific user pattern:
Invalid length for a Base-64 char array.
Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code.
Exception Details: System.FormatException: Invalid length for a Base-64 char array.
Source Error:
An unhandled exception was generated during the execution of the current web request. Information regarding the origin and location of the exception can be identified using the exception stack trace below.
Stack Trace:
[FormatException: Invalid length for a Base-64 char array.] System.Convert.FromBase64String(String s) +0 System.Web.UI.LosFormatter.Deserialize(String input) +25 System.Web.UI.Page.LoadPageStateFromPersistenceMedium() +101 [HttpException (0x80004005): Invalid_Viewstate Client IP: 213.199.128.155 Port: 24949 User-Agent: Mozilla/4.0 (compatible; MSIE 7.0; Windows NT 6.0; SLCC1; .NET CLR 2.0.50727; .NET CLR 3.0.04506; .NET CLR 1.1.4322; InfoPath.2; MS-RTC LM 8)
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We tried to use the ViewState Decoder and got the same error. During a discussion with the customer we found he was using an HttpModule to have a sort of custom logging to trace all incoming requests and outgoing responses… during the same discussion we browsed a few other working pages on the same site and doing some tests we found a difference in the viewstate produced.
To make the story short we notice a weird character sequence in the failing viewstates (=””) while in the working viewstates we never have two double-quote characters like that. Again using ViewState Decoder we tried to past the same failing viewstate but we changed the two last digits with two “equal” signs (==) and it worked…
This meant that something was touching the viewstate, and after some further investigation we found a problem in the custom HttpModule which under some circumstances was incorrectly adding the two double-quotes at the end of the string. Needless to say that fixing the bug also resolved the problem.
End of the story: if you search the Internet you can find a few viewstate decoders and loggers tools, give them a try if you find yourself in trouble with the viewstate, with some luck you’ll be able to quickly spot the problem and fix it. Of course, if this is not enough you can still call CSS?
Carlo
Quote of the day:
It may be true that the law cannot make a man love me, but it can stop him from lynching me, and I think that’s pretty important. – Martin Luther King Jr.