Urgent - Using virtuemart causes website unaccessable ( Fatal error )

[Hiboy]

After setting up my store, i access my website and it appear a white page with the following error :
Fatal error: Call to a member function getValue() on a non-object in /home/bryan/public_html/administrator/components/com_virtuemart/helpers/config.php on line 478

But when i put the store offline ,and remove the store at menu link ,my website is accessable. How do i solve the above error? I would wish to use virtuemart very much.

[jenkinhill]

It would help if you mentioned which versions you are using.

Around that line are the set language functions. Are you  using English in Joomla front end and in VM?

[huzaifadarbar]

Im also having the error,  but when I click vm menu link it gives me below error in only Chrome. it is not also consistent it goes on & off
"Fatal error: Call to a member function getValue() on a non-object in /home/content/~/administrator/components/com_virtuemart/helpers/config.php on line 478"

it work well in Firefox. But the error is only in Chrome.
Im using Joomla 1.5, Virtuemart2

Website :http://infra.darbarwebs.com/
error link on vm: http://infra.darbarwebs.com/index.php?option=com_virtuemart&view=virtuemart&Itemid=89