This is my transformation function call:
     <p><%# MyFunctions.getDocumentCategory(Eval("DocumentID"))%></p>This is the function:   
 public static string getDocumentCategory(int documentID)
    {
        string category;
        StringBuilder sb = new StringBuilder();
        // Get document categories 
        var ds = CategoryInfoProvider.GetDocumentCategories(documentID, "CategoryEnabled = 1", null);
        // Check whether exists at least one category
        if (!DataHelper.DataSourceIsEmpty(ds))
        {
            // Loop thru all categories
            foreach (DataRow dr in ds.Tables[0].Rows)
            {
                sb.Append(Convert.ToString(dr["CategoryDisplayName"]) + ",");
            }
        }
        string content = sb.ToString();
        category = content.Split(',')[0];
        return category;
    }
    }
This is the error:    
MyFunctions.getDocumentCategory(int) has some invalid arguments.
 I've tried an alternate form of the function that accepts strings rather than ints but it throws the same error. I've verified that the `Eval("DocumentID")` works correctly when placed by itself. Any ideas?