Excel newbie...

I have 2 spreadsheets. 1 column needs to be imported into another spreadsheet that has a lookup function programmed into it. Now when I cut-n-paste my data into it, the function is removed. How can I import my data without losing my lookup function?

I tried to recreate the function after I copied and pasted but I keep getting an error..

needed function as is...
lookup(A2,domain row,ns category row)

After I try to recreate I get an error...
#VALUE .. Error in value.


I'm taking a course in a couple of weeks but unfortunately, it's not soon enough for what I need to do. Any help would be appreciated.