Trouble passing Dates into stored procecure

Question

I have a J2EE (WebLogic) application that uses the jDriver to talk to a 9i database (mostly invoking stored procs). Most of the time they work fine, but I have one case in particular that has intermittent problems accepting Date objects.
The stored proc in question accepts 5 IN parameters (NUMBER, DATE, DATE, DATE, NUMBER) and returns one OUT param (VARCHAR). In the Java code, I have 2 Integer and 3 Date objects that I am setting on a CallableStatement to invoke the stored proc.
String SQL_TEMPLATE = "{? = call my_pkg.UPDATE_DATES(?,?,?,?,?)}";
statement = connection.prepareCall(SQL_TEMPLATE);
statement.setInt(2, int1);
statement.setDate(3, date1);
statement.setDate(4, date2);
statement.setDate(5, date3);
statement.setInt(6, int1);
statement.registerOutParameter(1, Types.VARCHAR);
As you can see, at no time am I converting between Date and String. However, sometimes when this code runs and executes the CallableStatement I get the following error:
"literal does not match format string"
I've done a lot of googling and from what I can tell that error should only come up if I was trying to use Strings and convert them to Dates.
The worst part is that this is not consistent. Sometimes it works fine, other times it fails. And when it fails it will continue to fail. Unless I give null for the Date objects, in which case it always seems to work.
I've tried it on different machines and by rebuilding/restarting the app numerous times - for example the most recent tests I did this morning it was working fine the first try, then I just bounced the app server (not Oracle) and then it started throwing the errors again. On a coworker's machine, the app works flawlessly every time (talking to the same DB instance); on another machine it worked at first, then exhibited the problem, but now works flawlessly every time.
I've tried moving to the thin driver which seems to alleviate this problem, but for various reasons that is not a real option at this time - I need to figure out what is wrong using the jDriver (OCI).
Does anyone have any insight as to what the problem could be? I'm desperate and willing to try just about anything at this point.
TIA,
Eric

Answer 1

Some new information that sheds a little bit of light:
I was able to narrow down the usage pattern that creates the problem. I start the app. The first save always works, regardless of which of the three Dates are non-null. After that, subsequent saves that only use non-null values for the same parameters as the first save will work. But if I try to use a real Date where I had originally saved a null, I get the error. If I restart the app, it starts over again.
For example:
A) Start app.
B) Save the form with Date1 and Date2 set, Date3 is null.
C) Go back and try to save the form again, this time with Date1 set, Date2 null, and Date3 set - ERROR.
D) Save the form again, this time going back to Date1 and Date2 set, Date3 is null - success.
I can repeat step D again and again with success. But step C will continue to fail (and other ones like it where I am trying to set a Date where I oringally set a null) until I restart the app.
Reminder: I am using WebLogic's jDriver (their own custom Type-2 JDBC driver that relies on the Oracle OCI client installed on the local machine)