Problem occurs when Group Digits on the textBox control is set to Yes. With this set to Yes, any number 1,000,000.00 or greater causes the error on save. With Group Digits set to No, any number works fine (entered without commas as Erwin advised in his answer). This problems occurs with the textBox in a snippet or directly in a dataView.
I have filed a ticket - number CC0000000101017
Did you enter the number with the thousand separators and the decimal separator? If so this issue can be reproduced when not using snippets. If you enter 2,000,000.00 this will lead to an invalid number entering the same number but as 2000000.00 the field will accept the number and place the separators so the field will show: 2,000,000.00 The issue does not seem to be limited to the snippets but rather that you can't enter floats with thousand separators. I suggest to file a ticket for this.
Mike, do you have any update on this issue? We're encountering the same problem...