Undoing user update of a field

Undoing user update of a field

I have two bits of code that are used for different subforms on the same form. The idea behind the code is to prevent the user from changing a field on a locked row (invoiced). The first code snippet works fine, the second gives an error.  Does anyone know why that would be?

1. if(row.Locked)
2. {
3. cd = PrintCustomisations[ID == row.ID];
4. if(cd.Height1 != row.Height1)
5. {
6. row.Height1=cd.Height1;
7. }
8. return;
9. }

vs

1. if(row.Invoiced)
2. {
3. info row.ID;
4. pp = PrintPublication[ID == Row.ID];
5. if(pp.Classification != row.Classification)
6. {
7. row.Classification=pp.Classification;
8. }
9. return;
10. }

Error