Prestashop 1.5.6, checkout leads to white page or to Technical Error

[patrmich]

Hi,

After upgrading to Prestashop 1.5.6, I am facing the following trouble :

In Back Office >Preferences > Orders

a- if I choose
for Order process type : "Standard Five steps"
and for Enable guest checkout : "Yes"
- in the FO, when clicking on "Cart" or "Checkout", the displayed page (http://www.site.com/order) is fully white

b- if I choose
for Order process type : "One-page checkout"
and for Enable guest checkout : "Yes"
- in the FO :
    - I click on the "Guest checkout" button, the following page displays : www.site.com/quick-order
    - I fulfil the delivery address, and click on the "Save" button
    - I get, on a small window, an error message :
        - TECHNICAL ERROR : unable to save account
            Details:
            Error thrown: [object Object]
            Text status: error

Thank you in advance for any help to solve those two problems.

Patrick