Trigger executing user stored procedure...

I use a usp that checks a given date...moves it past weekends and it checks the date against a holiday table...moving the date to the next business day. Heres the heart:
Create Procedure uspBusinessDays @startdate smalldatetime, @counter smallint, @NewDate smalldatetime OUTPUT AS
WHILE @counter > 0
BEGIN
SET @startdate = DATEADD(dd, @counter, @startdate)
IF DATEPART(dw, @startdate) BETWEEN 2 AND 6) AND NOT EXISTS(SELECT holidaydate FROM HolidayTable WHERE holidaydate = @startdate)
BEGIN @counter = @counter - 1 END
END
SET @NewDate = @startdate
GO
This is the procedure call from inside the trigger...the trigger passes the starting date and count to advance to the usp then gets the new date back to use in the table.
DECLARE @start smalldatetime, @DayCount smallint, @NewDateTime smalldatetime
SET @start = starting date SET @DayCount = 3
EXEC uspBusinessDays @startdate = @start, @counter = @DayCount, @NewDate = @NewDateTime OUTPUT
The trigger then uses @NewDateTime writting it to a table.
Now I've been using this usp for years with .asp. Now I need to fire a trigger to populate a single date field in a report table...which works great testing with query analyzer. Strange thing is...when the trigger fires...the DATEPART function works but the SELECT holidaydate doesn't! I've torn this apart twenty different ways and I'm exhausted!
Any ideas would be MUCH appreciated!
thx, rocker333

You've left out the interesting bit, which would be the code from the trigger that is calling this usp. Are you using DATETIME columns and variables all around?

Sorry...I've added those details now.
And to clear the mud...I've used uspBusinessDays for years without fail. I have webpages and other usp s calling it no problem.
Now I call it with a trigger...the usp advances through the weekends but doesn't ever match a holiday date.
[UPDATE!] I've found that by pasting the start date into the holiday table IT MATCHES and the process works! Now just gotta find a way to make sure all the date formats matchup!
I would appreciate any good tips on keeping my date formats matched!
Thx, rocker

Why would you ever worry about date formats?
-1- Make sure everything is declared as DATETIME.
-2- Never spell out dates in strings (unless you're writing to a text file).
-3- Never use CONVERT to remove the time part, but something like this:
DATEADD(d, 0, DATEDIFF(d, 0, GETDATE())).