Hi Kev,

Are you using or tried the ErrorProvider control? (find it in the
"Components" toolbox, or "All Windows Forms" toolbox)  This offers - by
default - a red circle "blob" + exclamation mark that will blink for a few
seconds and provide a tooltip of the error against any control you want to
have it.  E.g. textboxes, list controls, etc.  Remains invisible when not
set.

e.g. to set:
me.err.seterror(me.mytextbox, "My error text")

To clear a single instance:
me.err.seterror(me.mytextbox, "")

Validation can be done either on each control's change event (which I
commonly use, but it does depend on what you're trying to achieve), or after
a single large event, such as your change of tab page.  I would suspect you
would need to ensure that you re-select the tab page (if you have a set of
more than one tab anyway), so that the relevant tab is topmost and thus
visible to the user, then you would set the focus to whichever control on
the tab you want.

Hope that helps.

Al