Blank screen after sending Contact Form message : Override : Prestashop 1.6.1.18

[BrainSuperGlue]

Hi,

Our site too is having a huge amount of Russian email spam coming through. 
I have installed a reCAPTCHA module which required Overrides being activated to work. This I did.
Went back to the Contact Form and the typed a message, the reCAPTCHA works but after you click on Send, you should get the "message sent correctly" screen, however now I get just a white screen.

If I disable the reCAPTCHA module and disable overrides, all works again. I've tried many reCAPTCHA modules, does the same for all of them, so I don't think it's those.

Any ideas what could be causing the white screen?

Many thanks

BSG