edit a customers details and nochex prob

[Guest]

hi when i try and edit a customers details and save them this error comes up

 

Fatal error: Call to undefined function: customers_firstname() in /home/sites/site5/web/catalog/admin/customers.php on line 405

 

any clues anyone

 

also i am using nochex payment gateway the invoice amount does not come up when i check out

 

its set at ?0.00

 

please help