IsNumeric Variable Testing Function
You can only do numeric functions on numbers. It makes sense! Ensure that you actually HAVE a number before trying to work with it!
If your user input a variable that you put into BookCount, your syntax would look like this:
BookCountOK = IsNumeric(BookCount)
if BookCountOK = FALSE then
response.write "You didn't enter a number. Please try again."
ASP Variable Testing Functions