I have 2 versions of a VLOOKUP formula that are giving me problems, which I
fear may be related to the data. Excel 2003 running on XP Pro.

1st formula
=VLOOKUP(deviceserial1,[Calibration_Devices.xls]Sheet1!$A$4:$AM$33,2,FALSE)
2nd formula
=IF(ISBLANK(deviceserial2),"",VLOOKUP(deviceserial 2,[Calibration_Devices.xls]Sheet1!$A$4:$AM$33,2,FALSE))

Here is an sample of my data in column 1 of the specified lookup range.
28277
28937
30467
98982
50253098
2000/1C
3500/2C
A2211
A2365
A2432

Are my problems caused by the data being a mixture of alpha/numeric and
other characters? Whatever I set the cell format as doesn't seem to make a
difference. I have tried sorting this column in ascending order.