Can't make changes in configuration

Hi,

I'm building a new shop (or better: catalogue) in Hikashop. I installed the component few weeks ago, did some basic configuration and added categories and some products. Now I want to change someting in the configuration but I can't save anything. I get an error message that the checkout workflow is empty (but it's not, and it was not there that I wanted to make changes?) Shop is running in catalogue mode right now.
It also says 'no valid weight unit entered' and 'no valid dimension unit entered'.

After this error I downloaded and installed te newest version (1.5.7) but it still has the error.

What can I do? I really need to go on with this.
Thanks.