For uploaded or mailed cover letters, you do not need to include as much information as you would in an email message, because the heading of your cover letter includes your contact information. For a paper cover letter, use a formal business_style letter format which includes a heading, salutation, the body of the letter, closing, and your signature. Review these guidelines for what to include in your letter.
The second version is clearer and thus preferable. Of course, there are exceptions to every rule. What if you are the head of the Global Finance Team? You may want to get your message across without calling excessive attention to the fact that the error was your team’s fault. The passive voice allows you to gloss over an unflattering point—but you should use it sparingly.