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.
In the end, this is all about respect for your recipient. If you’re offering a real solution to a real problem, people want to know about it. By following proper and well_understood formats and keeping your writing clear and engaging, you’re making it easier for them to solve their problem. Provided that you’re honest and have the skills and talents to back up your claims, writing a good, solid letter makes it more likely that both you and your reader will be satisfied. Try it the next time you have to write an important letter.