(register and) checkout process fails in all details

[BartelBe]

Using Joomla 2.5.11 with PHP 5.4.16 I installed VM 2.0.22a multilingual FR and NL, and configured VM in detail (but without creating shopper groups, as I only need the default), delivery method is virtual, 2 payment methods: paypal and standard.

Cart functions just fine. But the checkout process simply doesnt work.  The required accepting of TOS can safely be ignored.   Forgetting the payment method is just fine for VM and when adding only the email address, hitting the button "register and checkout" allows a push. 
However (in-)complete you provide your input, you get the same blank page shop/user/editaddresscheckoutBT

I tried this in the website template but also joomla default templates, such as bees5 and bees2.  So I think I'm pretty sure it is not a template issue.

The website is: http://www.clouderp.be.  Any help is highly appreciated.

[BartelBe]

After 3 re-installation and removal of community builder (to make sure it is not a CB issue) I still have the very same issue.

I tested with and without demo data, I used the "renew with reconfig file", I tried reset and did clean installations.  I went to the demo admin site to doublecheck on settings.  All works fine, EXCEPT the user checkout and/or registration just don't work (except for the shop creator, where all functionality is as it should when buying)

Another thing I did:  I set the website to EN as  its main language and I installed VM in English only.  That too did not solve my issue.  But it enables you guys to access the shop in English and find out for yourselves, if you would invest your time to help solving my problem here.

Since I'm not a coder, I can't solve this issue on my own, but here is a clue.
As the shopcreator/owner, I can order and checkout and all control scripts, such as validation of accepting terms and empty field warnings work fine.
However, it does NOT work as any other customer, unregistered or registered.
Does anybody have a clue or can anybody reproduce this?

Thanks for your time.