From the screen shot that Steve Wilkins reposted, this looks like it may be an internationalization error between the software and your number entry.
If you live in a country that uses the comma "," as the decimal separator but have Windows set to use a period "." as the decimal separator, you will get just this sort of error. By entering whole numbers only, the error is avoided as you found. It can also be a problem with the reverse -- that is if you enter a period and your Windows installation is set for international format with a comma, then the same error will happen.
Try entering the decimal point in both formats and see if the error continues. If it does, maybe Ray will need to look at that section of code to make sure the conversion to decimal matches everything else.