I am setting up a sheet that when a code is entered elsewhere in the workbook
it fills the information in on a summary sheet.

For various reasons, we have a set number of lines (say 5) but if we only
enter 3 codes the other two show up as #n/a because there is no code entered
although the formula is there.

On the summary sheet we need to do a simple =sum() function but if one of
the cells contains #n/a then it won't calculate it.

Is there a way to get the sum function to ignore any cells which come up as
#n/a but to include them when it has a proper value?