Tedds for Word Error - Library not registered 0x8002801d

Problem

When trying to do one of the following 

1. Insert Calc Item from the Library Access System into Tekla Tedds for Word with the Add new Calc Section option checked
    
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or 

2. Send a Tekla Tedds standalone calculation to Tekla Tedds for Word

You may get the following error

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Information

If you are running Skype for Business 2016 but an older version of Office you will see the above error due to a problem in the Skype for Business install.  

The issue is not related to the Tekla Tedds installation but related to the use of Skype for Business 2016 and an older version of Office. It appears that the Skype for Business installation registers a primary interop assembly but doesn’t install the required COM libraries. Therefore it would stop any application that tries to use the COMAddin object from working properly.

Workaround

The workaround is simple

1. Repair Office
2. Remove the following key - HKEY_CLASSES_ROOT\TypeLib\{2DF8D04C-5BFA-101B-BDE5-00AA0044DE52}\2.8

Caution

Editing the registry directly can have serious, unexpected consequences that can prevent the system from starting and require that you reinstall Windows. Please ensure you are confident in what you are doing and also backup your registry before making any edits. It may also be prudent to create a restore point before editing the registry.

Further information

The issue explained in the following article and although it refers to the Word mail merge function the issue is the same for Tekla Tedds
https://support.microsoft.com/en-gb/help/3178867/word-mail-merge-doesn-t-work-after-you-install-skype-for-business-basi

Should you not have Skype for Business 2016 installed along side an older version of Office then please contact your local helpdesk for further assistance.