I can't install PrestaShop 1.6.1.18 (or 1.6.1.17 either) recently.
I get this error in the last installation step :
PHP Fatal error: Uncaught exception 'PrestaShopException' with message 'Property Currency->decimals is not valid' in */classes/ObjectModel.php:917
I am pretty sure it did work before, and I dont think I changed anything in my configuration.
PrestaShop version 1.6.1.x PHP version 5.6
Same issue for me. I solved it with this post : https://www.prestashop.com/forums/topic/743719-php-fatal-error-property-currency-decimals-is-not-valid/ :
I don't know which localization are you trying to install, i was installing the Italian pack. I think that Prestashop made some change to its localization files (in a wrong way), because if you go to http://api.prestashop.com/localization/16/it.xml (it's the file that presta try to import during the installation process), you can see that 'decimals' field is set to 2, that causes the error.
However after the first installation attempt, prestashop should copy this file in cache in order to use it next times, so try to go to /cache/sandbox/ and see if there is a file named 16{your_localization_iso}.xml and, if it exists, modify the currency line changing decimals form 2 to 1. It should fix the problem.
So, it seems a temporary trouble with the language packs download from Prestashop during the installation.
Merci !