Trouble adding session variable to insert parameter

I think my problem is with data types. The following line of code works if I substitute a number instead of session["userID"].ToString(). The parameter is type numeric in my stored proc. 
 My code:
cmd2.Parameters.AddWithValue("@userID", Session["userID"].ToString());
 For example, if I use cmd2.Parameters.AddWithValue("@userID", 55); my code works, so I think my problem is that I can't do ToString() because the parameter is type numeric in my proc. What can I do instead of ToString() with a session variable? Thanks
 
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