validation of numbers

Hi there,
I have installed CP Contactform with paypal on a site and am testing the free version of the plugin. I made a form for recurrent payments and tested this by making a payment of 1 cent every week for 3 recurrent happenings. It took some time but finally this worked well.
Now this morning I updated the plugin and then made a new form, cloning the first one and changing the payment in this new form to EUR 33,34 for 12 month
However the plugin insists the number should be either 33 or 34 “Please enter a valid value. The two nearest valid values are 33 and 34”

I tried 33.34 but that does not work either
Why does this not work. The form I made last week still works, it still accepts the 1 cent

cheers
Yolanda