I have a dropdown list in a page.
This list as the multiple selection option set.
So when a request the form data I get something like:

data1, data2, data3

no problem with that.
The problem is with my query.
I have a stored proc that take a parameter.
This stored proc is doing a Select statement based on the parameter with a IN statement.
Explanation:

SELECT
  *
FROM
  Test
WHERE
  Col.a IN (@parameter)

And, of course, the "@parameter" as the "data1, data2, data3" taken from my asp
page.
It's not working, unless I only have 1 selection from my dropdown list.
Is there a syntax specific or a special way of resolving my problem?