Problem with SQL query in Visual studio 2008

What is the value of @serial you are providing. Update that in your question. Syntax to me looks correct.

For SQL:
For verification try this if its work fine:

DECLARE @serial varchar(10)
SET @serial = 'A'

SELECT serial, company_name, ..., ...
FROM (table)
WHERE serial like @serial + '%'

For Code:

string serialThatStartWith = "S";
string myQuery = string.format("SELECT serial, company_name FROM (Sometable)WHERE serial LIKE '{0}%'", serialThatStartWith);

Try surround this like with "".

String.Format(" SELECT serial, company_name, ..., ...
FROM (table)
WHERE serial like '{0}%'", serial)

I don't know if i have typed it right but You should get the idea