An SQL database field was defined as CHAR(1). We used LINQ to SQL to expose in a web service, which defined the field as a System.Nullable
Unforuntately, it is not well known or well documented that “CHAR”s serializae and deserialize as the ASCII number, which is the equivalent of the character.
Thus is a BizTalk map, we had to use the Character to ASCII functoid to conver the letter “C” to the number “67”, in order to get BizTalk to properly build XML that is passed to a web service. When passing the letter “C”, you get a deserialization error.