Runtime error encodedvalue after log in using custom login FBA

Hi,

I have a problem when authenticating sharepoint site using claim based authentication where my custom login is a FBA located in LAYOUT folder. runtime error

Exception of type 'System.ArgumentException' was thrown.
Parameter name: encodedValue

shows when login successfully. Am I missing something in web.config configuration or something else should be in my attention?

FYI: my AD user has been added as Form authenticated in sharepoint site.

Any help and suggestions would be great.

Thanx

Edwin