Hi,
I'm afraid that there is no "format" function directly in the user views and we cannot reproduce your issue in our local websites.
Please check your PHP error log and set the "error reporting" to maximum in your Joomla global configuration.
We need to have more details about the error, specially the incriminated file and line (or the call stack).
Regards,
Jerome - Obsidev.com
HikaMarket & HikaSerial developer / HikaShop core dev team.
Also helping the HikaShop support team when having some time or couldn't sleep.
By the way, do not send me private message, use the "contact us" form instead.