Date Validation

All,
I have an application that needs to validate and convert a date from an
external system.
The format of the date can be m/d/ccyy,mm/d/ccyy,m/dd/ccyy,mm/dd/ccyy with
the "/" included.
The converted format needs to be a numeric field in the format ccyymmdd.

I have the following code in my program:
<snip>

// Edit Start Date

Monitor;

EpHOrDate = %Dec(%Date(Start_Date : *USA));

On-Error;

Load_Exception ('Start date is not a valid date');

EndMon;

// Edit Invoice Date

Monitor;

EpHInDate = %Dec(%Date(Invoice_Date : *USA));

On-Error;

Load_Exception('Invoice date is not a valid date');

EndMon;

</snip>
Where Start_Date and Invoice_Date are defined as 256A Varying and
EpHOrDate and EpHInDate are defined as 8p 0.

For values of 5/7/2012 for order date and 5/14/2012 for invoice date, the
code above rejects the order date, but accepts the invoice date.

I created a small test program to check the date editing process.
H Debug
D Date_in S 256A Varying
D Date_Out S 8 0
D Err S N
/Free
Monitor;
Date_Out = %Dec(%Date(Date_In : *USA));
On-Error;
Err = *On;
EndMon;

Return;

Using the values above, I set Date_In in DEBUG prior to the Monitor to each
of the dates.
BOTH of the dates were flagged as errors.

A. What am I doing wrong?
B. How can I handle the different date formats for editing and conversion?

The client is on V6R1M1

Thanks,