I have a very simple table of cost centre numbers and associated cost centre
names in the next column.
This table in a spreadsheet worksheet, links directly to our accounts package
through a template function supplied our accounts package supplier. This
table is fine.

V lookup is used in other workbooks to put the name in the next cell to the
cost centre number.
Vlookup will work, up to a certain cost centre number, but then, for no
apparent reason will displace the names by one line number. therefore, after
Cost centre 500, the name that applies to cost centre 490, the cost centre
immediately preceeding 500, appears in the adjacent cell, where you would
expect the name for CC500 to appear.

These lookups all worked fine, until I loaded Office 2003 SP 3 when the
problems started.