LINQ and Stored Procedures

Just starting off with LINQ, I've already found a strange behavior. In my SP, I have to select some blank columns, that used to exist in the table. Now, they're only there to stop old apps from crashing:

Select '' as inst from footable

This made Linq return only a cryptic error message:
System.FormatException: String must be exactly one character long.
at System.Data.Linq.DBConvert.ChangeType(Object obj, Type type)

But when I replaced the '' in the SP with a ' ' (that is, added a blank space) - everything works. So it looks as if Linq is trying to type every column in the result, and if it's empty, it dies.

Oh, and if you have a variable named @@foo in your script - I don't know why it was called @@foo, it just was - Linq will not be able to run it! It presumes that all variables are named @foo, which probably is the correct SQL, by the way. But - the error message, again, is not so helpful: The procedure expects the parameter "foo", which was not provided.