Instead of this
WHERE NOT ((@OldValue IS NULL AND @NewValue IS NULL) OR (@OldValue = @NewValue))
Try this
WHERE NOT EXISTS (SELECT @OldValue INTERSECT SELECT @NewValue)

^^ I agree with John.

Note that there is no need to precede a THROW statement with a semicolon.

Standard practice is to use Don't Save Sensitive and then use SSISDB environment variables to pass sensitive parameter values.

Note that it's been called SSIS, not DTS, since 2005.

So I suggest building your SQL dynamically via a package variable with an Expression and using that as the source for the ExecSQL task.

You cannot run anything more than very simple SQL against an Excel connection. The parameter stuff is probably causing the problem.