SqlCommand with wildcard parameter?

[Mark]

I have some code that starts with...

SqlConnection conn = new SqlConnection(Globals.ConnectionString);
conn.Open();
try
{
SqlCommand command = new SqlCommand("SELECT cusid, cusname FROM customer
WHERE cusname LIKE @Cna", conn);
try
{
command.Parameters.Add("@Cna", searchString);
SqlDataReader reader = command.ExecuteReader();
while (reader.Read())

If the string searchString contains the letter 'a' then this will run.
However, if searchString contains '%a%' (which uses tsql wildcard chars)
then I get the exception...

"An unhandled exception of type
'System.Reflection.TargetParameterCountException' occurred in
system.windows.forms.dll
Additional information: Parameter count mismatch."

and the debugger breaks on the "while (reader.Read())" line.

Anyone know whats going on here?

--
Best regards
Mark Baldwin
Software Developer