Hi Marc,
I think the confusion here is that DropColumns doesn't actually remove or delete columns from a data source. Instead, it returns a new collection that excludes the columns that you specify. For instance, if you were to set the data source property of a gallery control to the formula that you mention, you'll hopefully find that the gallery control doesn't show the SourceMatchName2 column.
To carry out what I think you want to do, you could collect the result from DropColumns into a new collection like so:
ClearCollect(CollectNewProjectAcct2, DropColumns(CollectNewProjectAcct, "SourceMatchName2"))
Alternatively, you could try to collect it into your existing CollectNewProjectAcct collection.
Hope that helps a bit.
