If statement within formula

[bopo]

Hi

Well basically, I have several vlookups which get data from another page, depending what ID number is entered int a specific cell, below is an example of one of the vlookup statements.

=VLOOKUP(B4, DataCustomerDetails!A8:L27,2,FALSE)

Now I would like an If statement (formula), which looks at the cell B4 for the value, then looks at the sheet named DataCustomerDetails for the value, if it isnt their, a messagebox should popup saying invalid ID or something.

Hel appreciated

[Bob Phillips]

=IF(ISNA(vlookup_formula),"Invalid,"vlookup_formula)