None of the archive email folders (PST) open to an account. ALL will not open. The lastest reached about 20 GB on Friday, then all became inaccessible even though they are individual pst files. I just see a tree list of folders and can not open the emails. Scanpst might chop away valuable mail. Any clue’s why this has happened? Or how I can retrieve the archives?

while the limit for a pst file in Outlook is no longer 2GB I believe that the size of your file is the problem. Either the file size alone or the file size in combination with the resources of your computer. 20GB is the maximum.
From http://www.pst.viewertool.com/

yup, your mail archive has exceeded the maximum size.
You MIGHT be able to open it with a later version of Outlook or Exchange.

A quick Google search for "recover outlook archive" yielded several tools that might help (mind, I've not tried any of them).

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