Unable to attach fields

Try manually adding an uploads directory to the plugin directory. It worked for me.
Example:
../wp-content/plugins/custom-contact-forms/uploads

I found the same problem, but here is how I got around it;

1. Sometimes I had to refresh the page after adding new fields/field items. This could be as simple as just clicking on the link in the left bar to go back to the forms page.
2. Most of buttons need a long mouse press before they actually work. Wait for the button to “depress” before letting go of the mouse button.