VLOOKUP with date as an argument
 

I have a problem !
In one spreadsheet I have in I152 a formula "I151+1", which formatted as a date gives me "30 nov 07" as a result.
In another spreadsheet I have an array where the same "30 nov 07" coming from a formula "Date(e6;11;30)" (where e6 = 2007), also formatted as a date.
I want to VLOOKUP a result in the second spreadsheet, with the date from the first spreadsheet as argument.
(It works without "FALSE" in the VLOOKUP-formula, but I want to make it work WITH this "FALSE". One never knows...)
Can somebody help me ?
Thanks in advance
Gilbert