Ignoring errors

Evening guys,

Any help on the issue would be appreciated.

I am using the formula:
=IF((AL6>AK6),"Y",IF(((VLOOKUP(AD6,LOOKUP!$A$3:$B$25,2,0))>(VLOOKUP(AB6,LOOKUP!$A$3:$B$25,2,0))),"Y","N"))

...and the formula:
=IF((AL6>AK6),"Y","N")

The formula works unless any of the cells are blank and then they give an error message. If anyone can suggest how I can alter each of the formulas so when the other cells are blank it just gives a blank cell rather than a formula it would be appreciated.

Many thanks for any help you can give.

Regards