Server Error in '/' Application.
Exception of type 'System.ArgumentException' was thrown.
Parameter name: encodedValue
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.ArgumentException: Exception of type 'System.ArgumentException' was thrown.
Parameter name: encodedValue
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:
[ArgumentException: Exception of type 'System.ArgumentException' was thrown.
Parameter name: encodedValue]
Microsoft.SharePoint.Administration.Claims.SPClaimEncodingManager.DecodeClaimFromFormsSuffix(String encodedValue) +600
Microsoft.SharePoint.Administration.Claims.SPClaimProviderManager.GetProviderUserKey(IClaimsIdentity claimsIdentity, String encodedIdentityClaimSuffix) +49
Microsoft.SharePoint.Administration.Claims.SPClaimProviderManager.GetProviderUserKey(String encodedIdentityClaimSuffix) +397
Microsoft.SharePoint.Utilities.SPUtility.GetFullUserKeyFromLoginName(String loginName) +10
Microsoft.SharePoint.ApplicationRuntime.SPHeaderManager.AddIsapiHeaders(HttpContext context, String encodedUrl, NameValueCollection headers) +927
Microsoft.SharePoint.ApplicationRuntime.SPRequestModule.PreRequestExecuteAppHandler(Object oSender, EventArgs ea) +437
System.Web.SyncEventExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute() +182
System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean& completedSynchronously) +165
Version Information: Microsoft .NET Framework Version:4.0.30319; ASP.NET Version:4.0.30319.18447
------解决思路----------------------
你做了什么导致错误发生？在网上找了几个同样的问题，看看是不是和你的情况一样：
http://sharepoint.stackexchange.com/questions/23996/exception-of-type-system-argumentexception-was-thrown-got-error-when-i-have
http://sharepoint.stackexchange.com/questions/13526/why-i-am-getting-a-following-error-while-implementing-custom-membership-provider
------解决思路----------------------
这很明显是一个系统报错的函数，检查引用，缓存等信息。
我原来也出现过。
按照这个方法试试，之前CSDN的帖子。
http://bbs.csdn.net/topics/90292438