Using DateTime in a SqlParameter for Stored Procedure, format error

I'm trying to call a stored procedure (on a SQL 2005 server) from C#, .NET 2.0 using DateTime as a value to a SqlParameter. The SQL type in the stored procedure is 'datetime'.

Executing the sproc from SQL Management Studio works fine. But everytime I call it from C# I get an error about the date format.

When I run SQL Profiler to watch the calls, I then copy paste the exec call to see what's going on. These are my observations and notes about what I've attempted:

1) If I pass the DateTime in directly as a DateTime or converted to SqlDateTime, the field is surrounding by a PAIR of single quotes, such as

@Date_Of_Birth=N''1/8/2009 8:06:17 PM''

2) If I pass the DateTime in as a string, I only get the single quotes

3) Using SqlDateTime.ToSqlString() does not result in a UTC formatted datetime string (even after converting to universal time)

4) Using DateTime.ToString() does not result in a UTC formatted datetime string.

5) Manually setting the DbType for the SqlParameter to DateTime does not change the above observations.

So, my questions then, is how on earth do I get C# to pass the properly formatted time in the SqlParameter? Surely this is a common use case, why is it so difficult to get working? I can't seem to convert DateTime to a string that is SQL compatable (e.g. '2009-01-08T08:22:45')

EDIT

RE: BFree, the code to actually execute the sproc is as follows:

using (SqlCommand sprocCommand = new SqlCommand(sprocName))
{
    sprocCommand.Connection = transaction.Connection;
    sprocCommand.Transaction = transaction;
    sprocCommand.CommandType = System.Data.CommandType.StoredProcedure;
    sprocCommand.Parameters.AddRange(parameters.To