I was having this same issue. I haven't investigated why this is happening, but in my project after commenting out the last interface in knockout.validation.d.ts the errors go away. This will break your call to isValid for validation though.
interface KnockoutSubscribableFunctions {
isValid: KnockoutComputed<boolean>;
isValidating: KnockoutObservable<boolean>;
rules: KnockoutObservableArray<KnockoutValidationRule>;
}
I added the following to get back the isValid function
interface KnockoutObservableBase {
isValid: KnockoutComputed<boolean>;
isValidating: KnockoutObservable<boolean>;
rules: KnockoutObservableArray<KnockoutValidationRule>;
}