DrawMerge does its best to prevent you from using options and numbering values that don't make sense ... to the other applications you use or to DrawMerge itself.
It may detect and warn you of a problem while you're entering information or once you click Go.
When there's a problem with the info you've just entered, it immediately displays a message explaining the problem and suggesting what to do about it. For example, it won't allow you to enter anything but numbers in the From: and To: fields.
In other cases, you may have entered valid information but some combination of information and options would cause problems for DrawMerge. In that case, it will display an explanation of the problem when you click Go. For example, if you've asked it to generate 1000 numbers and chunk by 300, you'll see a warning because 1000 doesn't divide evenly by 300.
At other times DrawMerge will be able to do what you're asking but it may not make good sense. In that case it still displays a warning message, but you'll have the opportunity to cancel or continue regardless.