Admin Page Gone Blank

Hi Everyone

Just had an issue in admin.

I set up a new coupon in Coupon admin for the new signup coupon. Then I went into Configuration ->GV Setup.

I selected the new coupon code and when I click on save the whole admin is now blank. The page seems to load but there is nothing on the page.

This is the second time this has happened and last time I had to restore a compelte backup for the fileset to get it to work.

What would be causing this problem. I want to set up this new coupon as I want the customer to spend a certain amount before the coupon will take affect.

Please help!!!!!!!!!!!!

Is there somewhere I can change this setting back to 0 for the new signup coupon????? (without going into the admin area - asits no longer there)

thanks

Tutorial link above then search for blank page

Hi

I searched as you stated in the tutorials sections, but it keeps saying about PHP errors.

I have not changed anything like that and all my changes have been through the admin.

Any other ideas....can I change the setting back to the way it was somewhere else as my admin is not coming up

Thanks

OK....it does help you read things properly......sorry my fault.....

I checked the cache for errors as stated and this is it below

[30-Jul-2010 14:49:47] PHP Fatal error: Call to undefined function: zen_date_diff() in /var/www/html/store/Bidgee182/includes/header.php on line 75

So I opened the file in question and this is what is at line 75

// if welcome email coupon is set and <= 21 days warn shop owner
if (NEW_SIGNUP_DISCOUNT_COUPON > 0) {
$zc_welcome_check = $db->Execute("SELECT coupon_expire_date from " . TABLE_COUPONS . " WHERE coupon_id=" . (int)NEW_SIGNUP_DISCOUNT_COUPON);
$zc_current_date = date('Y-m-d');
$zc_days_to_expire = zen_date_diff($zc_current_date, $zc_welcome_check->fields['coupon_expire_date']);
if ($zc_days_to_expire <= 21) {
$zc_caution_warning = ($zc_days_to_expire <= 5 ? 'warning' : 'caution');
$messageStack->add(sprintf(WARNING_WELCOME_DISCOUNT_COUPON_EXPIRES_IN, $zc_days_to_expire), $zc_caution_warning);

Just wondering what I have to change - bearing in mind I followed the tutorial to change the dates to dd/mm/YYYY from mm/dd/YYY

Check this

// if welcome email coupon is set and <= 21 days warn shop owner
if (NEW_SIGNUP_DISCOUNT_COUPON > 0) {
$zc_welcome_check = $db->Execute("SELECT coupon_expire_date from " . TABLE_COUPONS . " WHERE coupon_id=" . (int)NEW_SIGNUP_DISCOUNT_COUPON);
$zc_current_date = date('Y-m-d');