This button is only active when you have nintex forms installed along with Workflow. This is not meant to be used with

The Infopath form can be created separately. 

Regards,

Tomasz

Thank you for the response, hmm based on this thread it seemed like it was possible but perhaps not.  

What I need is to be able to have a different form for each a multi task workflow, mostly with attachments. Any thoughts on how to accomplish that using Nintex Workflow but Infopath Forms?

That post tells the truth - you are able to alter task form either using Nintex Forms or Infopath. BUT the button you are asking about will only be enabled when you have Nintex Forms app provisioned in current site

I'm afraid thats not true. Wouldn't make any sense to need Nintex Forms to use InfoPath on your workflows forms.

Maybe the following site collection feature hasn't been activated yet:

Can you please check that Jonathan?

Best Regards

Philipp

Philipp, I'm talking about the button on the task actions, which blows to launch Nintex Forms to manipulate with the task form.

The button Johnaton is asking about is not launching Infopath no matter what

Yes it does, at least on my machine. I tried it 5 mins ago on SP 2013 with InfoPath Designer 2013:

Both buttons are launching InfoPath

My apologies. I was wrong. I wasn't aware that this is possible even though I'm mostly often using Infopath rather than Nintex Forms to work with forms...

Thanks for the response Phillip, yes it seems this may be my issue. I do not even have this option available in the site settings area. This requires some type of configuration adjustment application server side?

It's a site collection feature so make sure you are looking it up at the right place (Site Settings -> Site Collection Administration -> Site Collection Features). You also need to be on the root web of your site collection to see the site collection administration options.

If you do not have this option available, you may need to contact your site collection admin to help you.

This was the resources I used to get it activated the reason I didn't see it is because I didn't have top level permissions to change it. 

Enable or disable site collection features - SharePoint