PayPal Express Checkout Error (10419)‏

Hi there
I am having a problem with accepting payments on my e shop
Few costumers try to purchase items and pay with paypal and it wont allow them ,it comes error message :
ALERT: PayPal Express Checkout Error (10419)‏
10419 Express Checkout PayerID is missing. - Express Checkout PayerID is missing.

I have contact paypal and they advise me that it is issue with zen cart itself not paypal

Could anyone please let me know what i should do ?
It is really important quick reply as i cant make sales till this is fixed and i am loosing costumer ,so i would appreciate quick reply.
Thank you
Kind Reagrds
Urszula

If you search the forums for 10419 there are a few threads about the same issue. A link to your site might let us spot something too.

Link to my site is http://www.luxurylingerieboutique.co.uk/
any ideas how to fix this issue?
:lamo: