checkout error

ver:2.1.0.2. Has been working well for months, and I don't recall making any changes recently.
I am getting errors when I try to checkout. It gets to step 5 and then throws 3 missing index lines and failing to display payment options as per:

Step 5: Payment Method
Notice: Undefined index: total in /mysite..../store/catalog/model/extension/total/sub_total.php on line 21
Notice: Undefined index: total in /mysite...../store/catalog/model/extension/total/shipping.php on line 24
Notice: Undefined index: total in /mysite..../store/catalog/model/extension/total/total.php on line 9
Please select the preferred payment method to use on this order.
text_title
text_title

The error.log is showing only those same 3 errors

Any help greatly appreciated.
Derek

text_title is showing due to your language ID on the platform that cannot be found due to an installed language pack or due to a failed upgrade process.

This path is valid for later OC versions:

catalog/model/extension/total/

On OC 2.1 it comes without "extension". Not sure how you did this, but you put your order totals in a wrong folder. Try to remove the files mentioned in error message and checkout again.

Thanks for the quick replies.
I had been trying to install a new store under V3. Judging by your responses it seems I must have somewhere in the procedures mixed up my stores. I will try to find what I did wrong.