'invalid memory address' error with go-mssql

I'm having an issue that I can't seem to resolve, probably due to my inexperience with GO. I have the following code working on one server, but not on another. Here is the code:

// Build out the connection string to the database, and then open the connection to the database.
connString := fmt.Sprintf("server=%s;user id=%s;password=%s;port=%d", *server, *user, *password, *port)
if *debug { fmt.Printf(" connString:%s\n", connString) }
db, err = sql.Open("mssql", connString)
if err != nil { log.Fatal("Open connection failed:", err.Error()) }
err = db.Ping()
if err != nil {
	fmt.Println("Cannot connect: ", err.Error())
	return
}
rows, _ := db.Query( "SELECT Zip FROM Zip_Rural WHERE Zip = ?", ZipCode[0:5] )
defer rows.Close()
if !rows.Next() {
	acreageRequirement = .5
}

On the line that reads if !rows.Next() I get the following error:

panic: runtime error: invalid memory address or nil pointer dereference
panic: runtime error: invalid memory address or nil pointer dereference [signal 0xc0000005 code=0x0 addr=0x20 pc=0x477918]

This same code works just fine on another server, running GO version 1.4.2 on both machines. I have a feeling I just have some bad syntax somewhere in here, but have no idea what the real problem is. A call to db.Exec within the same file works just fine, which leads me to believe that my database connection is perfectly fine, but for some reason db.Query is not executing correctly.

There is probably an error with db.Query. Check your error and if it is not nil, assume that rows is nil. i.e. calling rows.Next() will segfault.
If you display the error, you will probably find out what the issue is.