After upgrading to Umbraco 7.3.0, I am no longer able to log in using the Umbraco admin login screen located at /umbraco.

Have rebuilt, re-published and restarted the app pool, all with no progress. Your time an guidance greatly appreciated.

Error message reads:

Server Error in '/' Application.

Value cannot be null. Parameter name: value

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.ArgumentNullException: Value cannot be null. Parameter name: value

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:

[ArgumentNullException: Value cannot be null. Parameter name: value] System.Security.Claims.Claim..ctor(String type, String value, String valueType, String issuer, String originalIssuer, ClaimsIdentity subject, String propertyKey, String propertyValue) +11996035 Umbraco.Core.Security.UmbracoBackOfficeIdentity.AddUserDataClaims() +1229 Umbraco.Core.Security.UmbracoBackOfficeIdentity..ctor(FormsAuthenticationTicket ticket) +125 Umbraco.Web.Security.Identity.FormsAuthenticationSecureDataFormat.Unprotect(String protectedText) +87 Microsoft.Owin.Security.Cookies.