Using SQL Server 2005 and .NET 3.5.

I have a SQL stored procedure [collection and validation of parameters]
which references some CLR table valued functions [some complex mathematics].
The table valued functions, in turn, call a SQL stored procedure doing
simple data retrieval [the data needed by the functions].

If I execute the stored procedure from a query pane in Management Studio,
everything always works exactly as expected (regardless of which parameters
I pass to the procedure).  Any missing parameters are defaulted to NULL in
the procedure.

However, if the stored procedure is executed from either MS Access (using
ADO) or from a .NET application (using ADO .NET) strange things happen......

Sometimes everything works as expected.  However, depending on which
parameters are supplied, I sometimes see a .NET exception complaining about
an out-of-range exception from deep in my CLR code.  I have got to a
position where supplying or omitting one of the parameters consistently
causes the error to occur (or not).  However, oddly, the exception comes
from a piece of my code which should not be affected by that parameter being
present or not.

I have checked and double-checked that the same parameters are being passed
in through ADO (both flavours) and in Management Studio.  As I said,
Management Studio works consistently, ADO works sometimes.

Gut feel says that the issue must either be to do with permissions (although
that's not what the error says) or to do with ADO doing something odd with
the parameters.

I realise that I have painted only a very general picture here.  However,
I'd welcome any pointers on where my search should start.

Thanks.