Cannot login to brand new site collection (Microsoft.SharePoint.Administration.Claims error)

Hey Guys,

I've just setup a brand new SP2013 single server build.
I went through the whole setup without any problem.

At the end of the farm config wizard I created a first site collection.
When I want to browse that site collection I get the following cryptic error message below.

It is a brand new setup, nothing has been modified config wise.

I do not get why it complains about claims.
The server is part of my domain and I'm logging in with a domain admin account which is also in the local Admin group.
I can browse the CA without any problem.

Any idea?

Thanks

Server Error in '/' Application.
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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) +622
   Microsoft.SharePoint.Administration.Claims.SPClaimProviderManager.GetProviderUserKey(IClaimsIdentity claimsIdentity, String encodedIdentityClaimSuffix) +49
   Microsoft.SharePoint.Administration.Claims.SPClaimProviderManager.GetProviderUserKey(String encodedIdentityClaimSuffix) +481
   Microsoft.SharePoint.Utilities.SPUtility.GetFullUserKeyFromLoginName(String loginName) +10
   Microsoft.SharePoint.ApplicationRuntime.SPHeaderManager.AddIsapiHeaders(HttpContext context, String encodedUrl, NameValueCollection headers) +975
   Microsoft.SharePoint.ApplicationRuntime.SPRequestModule.PreRequestExecuteAppHandler(Object oSender, EventArgs ea) +456
   System.Web.SyncEventExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute() +182
   System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean& completedSynchronously) +183
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Version Information: Microsoft .NET Framework Version:4.0.30319; ASP.NET Version:4.0.30319.19030