I remember when the "pat-Error Could not load module base class" problem was an almost-daily occurrence. I searched through the forum and discovered that,
in every single case where this had been reported, the problem was due to using one of the old
Fireboard-style templates.
What particularly concerns me is that, ages after these problems first became apparent (in K 1.0.8, would you believe! :ohmy:) the current version of Kunena (1.5.

continues to ship the
default_gray,
default_red and
default_green templates even though they cause
other problems, they are not recommended for use and they are not supported! :S
In every case that I read, using the
default_ex template fixed this "pat-Error Could not load module base class" problem. However, maybe there's a new error that's been introduced in K 1.5.8 that deserves special attention? In order to see this situation at first-hand, would you be willing to give us the address of your website where the error now appears?
Thank you.