wpv-if won't work

Hi,

I am having trouble getting the wpv-if statement to work. Finally I set up a simple test case like this within a View template:

[wpv-if evaluate="1 = 1" debug="true"]
Text to display
[/wpv-if]

The text does not display. Instead I get an error message (translated from german): "The correct conditional expression could not be found."

Thanks for your help,
Florian