Problem with Klarna

Hello, in my new site http://www.cubecontrols.com i have installed your b2bking plugin.

Among our payment methods is Klarna and after the last release of your plugin it started not working, if I try to make a payment with Klarna, the checkout gives me an "internal Server error".
After several attempts and disabling my plugins one at a time, I realized that the problem comes from the B2Bking pro Version 3.9.5 plugin.

If I disable this plugin, the payment proceeds correctly.

How can I solve?
Thank you

Solved, there is an old version of b2bking pro.

Updating the pro version to 4 also solved the problem.
Thank you