The state information is invalid...

Ola pessoal, apos clicar em um botão do meu form, que é responsável pelo cadastro de usuarios acontece o seguinte erro..

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

Stack Trace:

[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 2.0.50727; .NET CLR 3.0.4506.2152; .NET CLR 3.5.30729)
ViewState: /wEPDwULLTE5MjI0NjMxMjMPZBYCAgMPZBYEAhEPDxYCHglNYXhMZW5ndGhmZGQCEw8WFB4TT3ZlcnJpZGVQYWdlQ3VsdHVyZWgeEUN1bHR1cmVEYXRlRm9ybWF0BQNETVkeIEN1bHR1cmVDdXJyZW5jeVN5bWJvbFBsYWNlaG9sZGVyBQNSJCAeFkN1bHR1cmVUaW1lUGxhY2Vob2xkZXIFAToeCkFjY2VwdEFtUG1oHgtDdWx0dXJlTmFtZQUFcHQtQlIeG0N1bHR1cmVUaG91c2FuZHNQbGFjZWhvbGRlcgUBLh4WQ3VsdHVyZUFNUE1QbGFjZWhvbGRlcmUeFkN1bHR1cmVEYXRlUGxhY2Vob2xkZXIFAS8eGUN1bHR1cmVEZWNpbWFsUGxhY2Vob2xkZXIFASxkZN8mPJOJiUiz3tssRM/4KWmPyUu/,/wEPDwUJODExMDE5NzY5D2QWAgIDD2QWAgIBDw8WAh4EVGV4dAUUNiBkZSBPdXR1YnJvIGRlIDIwMDlkZGQWHTWcQ58vc+JEnNPCY6isa7OjYQ==
Referer: [http://localhost:1459/Web%20Sellpro/cadastro.aspx
Path: /Web Sellpro/cadastro.aspx]

[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) +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.cadastro_aspx.ProcessRequest(HttpContext context) in c:\WINDOWS\Microsoft.NET\Framework\v2.0.50727\Temporary ASP.NET Files\web sellpro\b7527bc5\651d84b5\App_Web_7ajvnldd.24.cs:0
System.Web.CallHandlerExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute() +181
System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean& completedSynchronously) +75

E apenas no ff nao acontece..

Alguem poderia me ajudar?

Obrigado desde ja.