You attempted to decode an improperly formed URI (Uniform Resource Identifier). URIs have a special syntax; most non-alphanumeric characters must be encoded before they can be used in a URI. You can use the encodeURI and encodeURIComponent methods to create a URI from a normal JScript string.
A complete URI is composed of a sequence of components and separators. The general form is:
The names in angle brackets represent components, and the ":", "/", ";" and "?" are reserved characters used as separators.
To correct this error
Ensure you are trying to decode valid URIs only. You cannot decode normal JScript strings, as they may contain invalid characters.