Vista - Typed Dataset looses Data

Afternoon,

I have developed a winforms application used by around 1000 users.
The
application is used by engineers to view scheduled maintenance work
on
thier laptops. It uses a typed dataset to store the users work orders
and saves it on the users laptop via binary serialisation. The server
hosts a webservice with a MS SQL database back end and it uses xml to
send/recieve work orders and other data when the client application
is
connected to the network.


I have seemingly random problem, where by the dataset looses items of
data.


A typical senario is when a user books time accross a number of jobs.
I create a new row in the datatable and populate it with the time
details an a hard coded row number, add the row to the datatable and
accept changes. If connected the application then converts the
datarow
to xml and uploads it to the server (on a separate thread). However,
as the application builds the xml it gets an error stating the row
number is dbnull.


This is a sporadic error and I haven't as yet been able to replicate
it, however, I get a simular error with 2 other columns in two other
tables in the dataset and again the values input are safe guarded to
ensure a null is never entered into the column.


Has anyone ever experienced something simular? Any clues as to what
is
happening?


Many Thanks


Fran