I can't create a structure

Hi, I've installed solidres but when I'm going to create a new structure I recive a blank page.
I attach a screenshot

penso che prima devi creare una categoria
es. hotel

I've created a category named "B & B". I've tried some names but the problem remain

ITA: ho già create precedentemente una categoria nominata "B & B". Ho provato anche altri nomi ma non cambia nulla.

I resolved upgrading joomla to latest version.
The back end side works perfectly but on the front side if i check the availability I recive this error:
Fatal error: Class 'SRCurrency' not found in components\com_solidres\views\reservationasset\view.html.php on line 52