random errors with ado and ms access

I have an application that runs on Win 98, MS Access 2000 and a Delphi 6
based program. The program uses ADOConnection, ADoTable and ADOquery
components. Most settings i have left to there default values.

Just recently we have been getting a large percentage of random errors:
'external exception error c000006'
'could not update table, currently locked'
'MS Jet database engine cant find the input table or query'.

The database opens fine in Access and to my knowledge hasn't changed,
has the Delphi based program. The network does go through stages of running
very slow however, almost appearing to freeze, even with nothing running but
the desktop.

I don't have exception handling in some routines, for example:
with datamodule1.scoresADOTable do
                   FieldByName('username').Value := username;
                   FieldByName('date').value:= timedate;

So my questions are:

Should i have try/except on every database instruction? ie
try datamodule1.scoresADOTable.FieldByName('username').Value := username;

What sort of things should i be doing in the 'except' part of my program?

Can i just increase the value for connectionTimout/commandTimout properties
of the ADOConnection, ADOTable and ADOQuery components?

Could any of the other properties be set incorrectly and thus cause these

Many thanks for any help given, its driving me barmy :(