Can this man sue an artist for copyright infringement on a song they wrote/recorded together?

This is a very complicated question -- you should seek the advice of competent entertainment counsel and not rely solely on any answer provided herein for legal advice.

That said, your assumption that each writer of a musical composition owns an undivided interest in the entire copyright in the song is correct, as is your assumptin the he or she generally has the right to issue a non-exclusive license to use the song. The obligation of each co-writer is to account to and pay the other co-owner his or her share of royalties received from any exploitation. That's one of many things which songwriters generally do not understand when they create a joint work with another songwriter.

But the failing in your analysis, however, derives from the fact that you are not considering the very different issue of the sound recording copyright, which is a right that is distinct and separate from the copyright in the musical composition. The sound recording of the musical composition can be, and often is, owned by someone other than the owner of the musical composition copyright.

So your analysis should begin with the question, "who commissioned and/or paid for the sound recording?" and who owns it? Generally speaking, a record company will pay for the studio time and, usually by contract, own the sound recording copyright as a work made for hire. In instances where a band gets together to record a song and collectively pay for the studio time, the generally accepted principal is that each member owns an undivided interest in the sound recording absent a written agreement to the contrary. Now, to return to your original question, if the sound recording is owned by the second artist, then he or she may very well have the right to prevent the first artist from distributing and/or performing the sound recording via YouTube. If they jointly created and paid for the sound recording, then the analysis returns to a jointly-owned copyright, for which each owner has an unfettered right to issue license, and the second artist would likely have no rights to restrict the first artist from putting it on YouTube.

The second part of your question, involving the "company" that was chartered months after the recording took place, is a question of corporate law. While a corporation (or LLC if that's the case) cannot enter into contracts prior to its formation date, a person who is organizing the company could, in theory, enter into contracts prior to formation and then assign the contracts to the corporation. It doesn't sound as if this is the case in your instance, but I am without sufficient facts to make that determination.

Again, check into hiring a good lawyer who practicies in this area.

There's not much to add to Barry's thoughtful analysis.

It's useful -- I would say required -- for songwriters and musicians to educate themselves on copyright law. For less than $15 your friend should buy a used copy of "Moser on Music Copyright" via amazon.com and read it cover to cover.

I'll only add a bit of information about the very often misunderstood "work for hire" doctrine. The doctrine is a mechanism to establish the ownership of a copyright.

Two fundamental rules must be understood first: (1) the copyright to a work initially vests in the author(s) of the work and (2) the author(s)' copyright can ONLY be transferred to another person by way of a written agreement.

With those rules in mind, Section 101 of the Copyright Act creates TWO types of “works made for hire.” The first is ANY copyrightable "work prepared by an employee within the scope of his or her employment." So, when an employee creates a copyrightable work the employer is automatically the "author" of the work and owns the copyright in that work -- no written agreement between the employee and employer is required.

The second type of "works made for hire” are works that are "specially ordered or commissioned" AND which fall within one of the eight categories of "works" that are listed as qualifying as specially ordered works for hire. Those eight categories are (1) a contribution to a collective work, (2) a part of a motion picture or other audiovisual work, (3) a translation, (4) a supplementary work, (5) a compilation, (6) an instructional text, (7) a test, answer material for a test, and (8) an atlas.

Literary works (such as musical compositions -- "songs") and Sound Recordings are NOT listed among the eight categories of works that qualify as specially ordered works for hire. In short, the copyright to songs and the copyright to the sound recordings of songs CANNOT be transferred as specially ordered works for hire as the uninitiated (or devious) often try to do via a "work for hire" agreement. Those copyrights can be assigned (i.e., transferred or "sold" to another), of course, but the document that conveys those copyright interests is an "assignment" agreement. The terminology distinction is important because the work for hire doctrine has no relevance to the transaction.

Unlike work for hire agreements, copyright assignment agreements can statutorily be terminated after 32 years (i.e. the copyright "reverts" back to the creator of the work if certain procedural requirements are met). Which is why the music industry (record labels and music publishers) has historically, and arrogantly, simply considered song and sound recording copyrights eligible for transfer as specially commissioned works for hire. That is not the law, however. And they, and the courts, know that such works must be transferred by assignment agreements. [The record labels lamely argue that sound recording copyrights are "collective works" which are one of the eight listed categories of works subject to transfer via a work for hire agreement).

In practice, studio musicians often own no copyright interests in the sound recordings they help create because they're employees (of either the studio, the record label, or the band on whose album they are performing). And some musicians are obligated via their conduct and relationship with other musicians to sign an assignment agreement that conveys their copyright interest in their creations.

BUT for the vast number of musicians who are neither employees nor who have agreed in some enforceable manner to transfer their rights in the music they create, the copyright in their creations remains firmly with them as authors or co-authors. Barry has already very ably discussed the rights of co-authors. Another issue for copyright owners to think about is whether they have, through their words or actions, actually or impliedly licensed someone else to exploit the copyright in their song or sound recording