CC @seanbudd

Steps to reproduce:

1. Download an add-on from an external source
2. Open the add-on from explorer

Actual behavior:

ERROR - unhandled exception (08:45:34.803) - MainThread (12336):
Traceback (most recent call last):
  File "wx\core.pyc", line 3407, in <lambda>
  File "gui\addonGui.pyc", line 578, in handleRemoteAddonInstall
  File "gui\addonGui.pyc", line 482, in installAddon
ModuleNotFoundError: No module named '_addonStoreGui'

Expected behavior:

Add-on is offered to install.

System configuration

NVDA installed/portable/running from source:

Installed

NVDA version:

alpha-28398,7d716373

Other questions

Does the issue still occur after restarting your computer?

Yes

Have you tried any other versions of NVDA? If so, please report their behaviors.

Did work before the add-on store was merged.

If NVDA add-ons are disabled, is your problem still occurring?

Yes