When you fill cells with vlookup formula content when the vlookup source file
is closed it can be very slow. Why not have the program check to see if the
source is open first. If it is not then check system resources in connection
with the file size to guess whether or not there is sufficient system
resources to open it. If it seems reasonable that opening the file will not
place an undue load on the system, HAVE THE SYSTEM OPEN IT IN THE BACKGROUND
WITHOUT THE USER'S PROMPTING. If it is more likely place an undue load on
the host system's resources, have the user the user make the choice.

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