Queries :: Failing To Filter By Criteria After Return Values From A Function?

I have two date fields in a table. I need to find the days between these dates and, if its greater than 7 days, I want to display the record in a report, so far, I have found a hand function that allows me to enter two dates and it returns a long data value representing the number of days in between the two dates. (google "I've developed the following code to count the business days between 2 dates." and its the second one that starts as SOLVED I made no mods to it as it does what i need it to do.

So, i added this to its own module within the data base for use within a query. My test query basically displays the unique ID, the start date and the end date and then displays the values returned from the function. here is the SQL:

SELECT [Main Table].[Unique ID], [Main Table].[Start date], [Main Table].[End Date], (Business_Days_Between([End Date],[Start date])) AS [Days between]
FROM [Main Table]
WHERE ((([Main Table].[Start date]) Is Not Null) AND (([Main Table].[End Date]) Is Not Null));

When ran, this Query works... However, when I enter a criteria like =2 or > 7, it says data type mismatch. I have even attempted the CInt() function to make sure its formated as int but i continue to get the same error.