OpenSP: An attribute value must be a literal unless it contains only name characters
You have used a character that is not considered a "name character" in an attribute value. Which characters are considered "name characters" varies between the different document types, but a good rule of thumb is that unless the value contains only lower or upper case letters in the range a-z you must put quotation marks around the value.
Put double quotes around the value.
Unless you have extreme file size requirements it is a very good idea to always put quote marks around your attribute values.
- W3 validator: http://validator.w3.org/