Hello,
Hopefully I have tagged this right...first timer...
Into the code below I have added AddColumn(Close,"Close",1.2);
When I run the exploration the closing price column is visible until the exploration finishes then the Close column disappears...help please!!
// Downloaded From www.Wise****.com
// Formula removed as coming from illegal site
Do not use random AFLs that floats all over the internet. Most of them are written either obnoxiously or are just copy-pastes of someone else's sweat. Use legitimate AmiBroker sources please.
No more spoon-feeding, you will have to find the reason on your own and share the solution here. 
The code you downloaded is simply wrong. "WiseStock...." is a SCAM site which steals formulas and publishes them without permission. The formulas that can be found there are either incorrect or illegally copied from somewhere else. Posts with formulas found on "Wise...." are forbidden on this forum.
And AddColumn just works:
Filter = 1;
AddColumn( Close, "Close" );
That's it.