Error after upgrading to version 2.3.0.2

I have upgraded from version 1.5x to version 2.3.0.2. My php server version is php5.6.
I get the following error : Warning: Parameter 1 to ModelTotalSubTotalTax::getTotal() expected to be a reference, value given in /home/x12xcmpt/public_html/system/engine/loader.php on line 178
When i am trying to acces my website : www.exe-computers.ro.
The admin dashboard section is working fine. I couldn t fiind any help related to this so far, so maybe someone here can help.
Thank you

I have upgraded from version 1.5x to version 2.3.0.2

well, hopefully NOT by use of this Information, because as it clearly
mentiones, to only work for updating OpenCart V1.5.x TO LATEST OpenCart 1.5.x
But just don't come back, and ask me, why this File still exists in the latest OC v.2.3 Download,
no-one around here would know. Exept, possibly, the Chief in OC-Command. But keep this as
a Secret, he get's up tide easy and fast, if someone sounds, just like me right now...
So, if you never see me here again, you at least know why...
Good Luck!
Ernie
///////////////////////////////////////
/// OpenCart V1.5.x TO 1.5.x ///
/// Upgrade Instructions ///
/// http://www.opencart.com ///
///////////////////////////////////////
NOTE: THIS IS FOR UPGRADE ON EXISTING INSTALLS ONLY!
IF INSTALLING NEW, BE SURE TO READ THE INSTALL.TXT FILE INSTEAD
##########################################
THIS IS FOR UPGRADING EXISTING OPENCART 1.5.x STORES ONLY
THIS IS FOR UPGRADING EXISTING OPENCART 1.5.x STORES ONLY
THIS IS FOR UPGRADING EXISTING OPENCART 1.5.x STORES ONLY
##########################################