RegularExpressionValidator failing in I.E.

Hi,
I'm trying to use a RegularExpressionValidator control with this expression "^(?=.*[#$_@!£&]).{8,19}$" to validate passwords so that it must have at least 8 characters and also have one of the following characters # $ _ @ ! £ or &.
This works fine in Firefox but on Internet Explorer it always fails. Any ideas?

Thanks
Sidharth

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