A family of Microsoft spreadsheet software with tools for analyzing, charting, and communicating data.
VLOOKUP is no the cause, see screenshot below.
B2: =VLOOKUP([@[Opportunity Num]],D:E,2,0)
The error message comes from elsewhere.
If you need further help please upload your file (maybe with anonymous data) on an online file hoster like www.dropbox.com and post the download link here.
A macro to anonymize data in selected cells can be downloaded here:
https://www.dropbox.com/s/rkfxuh85j5wyj9y/modAn...
Andreas.