Why do other apps - particularly IE interupt excel VBA
 

I have a VBA application that I'm writing that will be used by several
other users - so I obviously can't restrict them from running other
applications.

I've noticed that if I launch another application - particularly IE or
another Excel shell that my VBA code is interupted - generally when it
is in the processes of opening and reading a series of Excel data
files.

It tends to happen less often if the applications were started before I
start the VBA code, but it still happens.

Any suggestions?