Symptoms

After working properly for some time, clicking the Attach (or paperclip or Insert) button in the email application brings up the applications regular file selection dialog instead of the Attach Plus file selection dialog (in other words, the Attach Plus button is missing from the file selection dialog).

Before continuing, please make sure that Attach Plus is actually running and that the problem still happens.

Background

If a plugin to Outlook has changed the behavior of the Attach button, it will prevent Attach Plus from properly intercepting the mouse click.  We know for certain that Winzip has an Outlook add-in that causes this problem.

To test, launch Outlook in Safe Mode and see if the problem goes away

Also, refer to the following related articles:

Paperclp integration does not work after installing the Zimbra connector

Paperclip integration does not work after installing ShareFile addon for Outlook

Resolution

Uninstall the Outlook add-in that is causing the problem