Try the following:

• Install with anti-virus disabled
• Install with firewall disabled
• Install on clean boot
• Install as Administrator (right-click on setup icon)
• Bypass any proxy servers

Hope this help!

If you download the updated program file (10.0.6.31) by visiting the 'Download' section of your profile (drop-down menu at top-right of this screen), then you can install over the top of your existing version.  Reboot your PC, and run the setup file whilst X5 is closed.  Right-click on the program icon and select 'Run as administrator'  -  you won't lose any data.

This is a preferred way of updating the program if other issues (antivirus, firewall, etc) prevent you from updating within the program itself.

Regarding the Guestbook error, here are a few things to check:

• The page that your Guestbook is on must have a .php extension, as opposed to a .html extension, for example
• Your server must support PHP  -  you can check if this is the case by logging in to your Website X5 online control panel as described here: http://help.websitex5.com/en/index.html?pannello_controllo.htm
• X5 must be able to write to the Guestbook folder on the server.  Check the folder permissions on the server for the folder in question
• If you specify a 'Server folder with write access' in Step 3 - Guestbook Object properties, then that folder must physically exist on the server.  You may have to manually create it if necessary

You can create 'Options' for each product that you sell in your online store, in your own case 8x10, 16x20, etc.  -  this is done on the 'Products' tab of the 'Shopping Cart' in Step 4 Advanced Settings.
First you must create at least one product...  then click on the 'Edit' button on the right of the screen...  in the screen which opens select the 'Options' tab...  the help file is here:
http://help.websitex5.com/en/index.html?carrello_prodotti_imp_prodotti.htm
Hope this helps!
Paul