see my following post https://community.nintex.com/message/42747?commentID=42747#comment-42747 

Hi,

function GetNumberOfAttachments(attCtrlClassName){  
return NWF.FormFiller.Attachments.GetAttachedFilesCount(NWF.FormFiller.Functions.GetFillerDivObjectForControl(NWF$("#"+NWF$("." + attCtrlClassName + " .nf-attachmentsRow")>0].id)).data('controlid'))  
}  
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I'm new to JavaScript so could you please explain this, including where to put this code (I assume Form Settings > Custom Javascript).

Thanks.

yes place the code into custom javascript.

configure for attachment control you want to check  'attCtrlClassName' CSS class (without quotes)

set up a validation rule with formula: Question1 = "Option 2" && GetNumberOfAttachments("attCtrlClassName") < 1

configure for attachment control you want to check  'attCtrlClassName' CSS class (without quotes)

I still don't understand this step. I don't see how a CSS class could do anything. Could you please provide screenshots?

I have done this and it's still not working. Am I doing something wrong?

if I count braces in your formula correctly you miss there one closing brace that would close and() ...

Thank you! It works now.

Only problem is that now that the CSS class has changed, I've lost my blue background on the attachment control; is there a way to access the attCtrlClassName CSS code to modify it? The CSS I was using before was nf-form-input nf-section.

Also, if could you please explain the separate parts of the javascript code it would really help. Thanks.

hurray! 

Only problem is that now that the CSS class has changed

this is not a  problem, you can define as many CSS classes as you need.

so, add all the needed classes separated by space, like "nf-form-input nf-section attCtrlClassName"

is there a way to access the attCtrlClassName CSS code to modify it

the class has no definition (OOTB). it's just used as a identifier for the control.

if you want/need you can define whatever styling to the class you need

if could you please explain the separate parts of the javascript code

there is not too much to explain, I just used two built in NINTEX's functions which identified attachment control by its classname and returns its number of files .

Thank you