Invalidate date in Sitemaps

I have a forum running vBSEO 3.5.1

Google webmasters is reporting a invalid date for some of the URL's
I had a closer look at the URL's and these all refer to the Forum Category

The lastmod data is like this:

Code:

<lastmod>1969-12-31T18:00:00-06:00</lastmod>

The date is set as 31 Dec 1969 for all the category URL's in the sitemap XML
The thread/post lastmod dates have no such issue

How to fix this?

Hello ,

I don't see a vBSEO license assigned to your username. If you purchased vBSEO please PM me your payment transaction id and forum url so i can correct your license status.

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