MVC3 Regular Expression Validator - "Syntax Error In Regular Expression"

JScript is Microsoft's version of ECMAScript, which supports an extremely limited set of regex features compared to .NET. Your biggest problem is that it doesn't support inline modifiers like (?i:xyz). There also seems to be no way to pass modifiers separately, like you could if you were using C# or JScript directly. If you want to exclude things case-insensitively, you're kinda screwed.

Be aware, too, that character-class shorthands like \d and \W have different meanings on the server (.NET) than they do on the client (JScript). If you want the regex to work the same on both sides, you might want to be more specific. Here's an example, broken down for clarity:

^
(?=\S{8,}$)           # eight or more non-whitespace characters
(?=.*[0-9])           # at least one digit
(?=.*[a-z])           # at least one lowercase letter
(?=.*[A-Z])           # at least one uppercase letter
(?=.*[^A-Za-z0-9])    # at least one non-letter, non-digit
(?!.*(?:pass|word|god|PASS|WORD|GOD))
.+$

As you can see, I'm only excluding all-lowercase or all-uppercase versions of pass, word, etc., which isn't really satisfactory. If you really need to exclude or require whole words case-insensitively, you may have to use a different kind of validator.