I have these 2 formulas in a workbook in Excel 2003:

A)=IF(ISBLANK(deviceserial2),"",deviceserial2)

B)=IF(ISBLANK(deviceserial2),"",VLOOKUP(deviceseri al2,'C:\Calibration
Masters\[Calibration_Devices.xls]Sheet1'!$A$4:$E$31,5,FALSE))

When named range deviceserial2 is blank, formula A displays nothing (as
intended) and formula B displays #VALUE. When the named range is completed
with a serial number, it again displays properly with formula A but displays
#VALUE again for formula B.

If I change formula B replacing the second instance of deviseserial2 with
the actual cell address it works fine except when there is no serial number
in the cell, instead of nothing it displays a zero.

I cannot see where the problem lies with this and amlooking for any pointers.