Thank you for this question.
RadSpreadsheet by default uses the system defined decimal separator. In 2013 Q1 Service Pack there is a known issue that our control cannot parse an expression if the current decimal symbol is different from a dot. This is the case with some languages, as German, French and others, which use a comma as decimal delimiter.
Fortunately, we have already managed to resolve this problem and the fix is available in our latest internal build. We are also going to upload our online demo with this fix, so it will work as expected. In the mean time you could change the decimal symbol of your culture (see attached picture) in order to give a try to our example.
I hope this information helps. Please, do not hesitate to contact us if you have any other questions.