_getAmountPrice function doesn't exist error

Hello friends,
I have oxid CE.
I am getting errors:
1)_getAmountPrice function doens’t exist!(oxArticle).
2)getAllSets function doesn’t exist!(Order)

I have found the definition of both the function inside oxarticle.php and payment.php respectively. It means that error could be regarding to the usage.

If any of you have any idea, help me on this. I am really frustrated now. I am unable to run my system due to these problems. Help me!!! I highly appreciate your help

Thanks
Gyan

Do you try to call these functions from a specific template file and have you modified any files?

Or are you getting these errors with Oxid-standard configuration?

If you have modified something or try to get special behaviour by calling these functions you should give detailed information about the modifications you have made.

I have standard configuration.
The first error pops out when I click on something to open on the left hand side categories option.
And the second error is occurring at the 4 step of the payment.

I appreciate your taking time to help me.
I look forward to your response.

If you have changed nothing to the system, maybe something went wrong during installation. Have you tried to reinstall the system from scratch. Take care about the System requirements.