/admin blank page

Hi Guys,

Ive got a problem, my Opencart site was working fine, however ive recently done a move from Hostgator to Bluehost.com and they migrated the site over with all the files and restored the databases.
The config files were changed to point to the correct databases/usernames and the website is working great.
That was until i noticed i could no longer access the mydomain/admin area

When i try to access it just comes up with a blank page!
Ive spoken to their tech support and they say its because of the below error in VQMod and i cant really seem to get any more help from them about it:

[18-May-2014 05:30:20] PHP Fatal error: Call to a member function getId() on a non-object in /home2/whitedr8/public_html/vqmod/vqcache/vq2-catalog_controller_common_header.php on line 50

line 50 in that file shows:
$this->data['text_report_sale'] = $this->language->get('text_report_sale');

Can anyone be so kind as to help me fix this as im not the most tech savvy person?
It was all working fine until the migration to Bluehost and im not sure where to go from here

Many thanks,

check for line 50 in this file:vqmod/vqcache/vq2-catalog_controller_common_header.php, instead of the original file.
Post the code in line 50 here. I will see if I can help.

Hi, thanks i've pasted line 50 below:

$this->model_tool_online_plus->whosonlineplus($ip, $this->customer->getId(), $url, $referer);

Two things to do:
(1)Reinstall vQmod by visiting in a web browser http://domain_of_your_site/vqmod/install
(2)check if system\library\customer.php is there. If it is there, the customer.php file might be corrupted. So reuploadding system/library/ folder from your local one might help.