Why does the message "The object reference was not set to an object instance" appear?

Solution:

The email client must have all the defaults in the control panel.

Follow these steps for Windows 10 (older operating systems may differ):

1. Open the Control Panel
2. Open the "Default Programs
3. Click on "Set default programs"
4. For the default "Email" app, select your email client. It may also help to temporarily select a different email client and then switch back to the correct one.
5. After that, scroll down and click on "Set default settings by app".
6. Locate your email client, click on it and click on "Manage".

Finally, select your email client from the list of possible file type and protocol mappings for each option.

If these steps do not help, you can still check the registry.

XPhone Connect searches for the default email client in the following registry keys:

HKEY_CURRENT_USER\Software\Clients\Mail

HKEY_LOCAL_MACHINE\SOFTWARE\Clients\Mail

HKEY_LOCAL_MACHINE\SOFTWARE\WOW6432node\Clients\Mail

On the right side of the key "(Default)" is the name of the default e-mail client. If there is not the desired e-mail client, replace the value with the correct e-mail client. Use the name of the respective subkey of HKEY_LOCAL_MACHINE\SOFTWARE\WOW6432node\Clients\Mail as independent keys, e.g. "Microsoft Outlook" or "IBM Notes".

If this does not solve the problem, check whether the Microsoft Office installation on the affected workstations was still 32-bit at the time of the XPhone Client installation and has now been changed to Microsoft Office 64-bit (or vice versa, if applicable), possibly in the course of an update to a newer Office version. If this is the case, perform a repair installation for XPhone Connect Client. This is necessary because the Microsoft Office platform is determined dynamically during the installation (32- or 64-bit) and thus the appropriate components are installed. During a repair installation, this detection is run again and the installation is corrected accordingly.