Daryl Hall Suing John Oates in Mysterious Lawsuit

Hall & Oates, one of the most successful and iconic duos in musical history, are not just on the outs ... they're in litigation.

Daryl Hall has filed a lawsuit against his former musical compadre John Oates, claiming some form of breach of contract.  What's more, Hall got a restraining order against Oates this past Friday.

As for the details ... well, the court file is sealed, but we have been able to piece together some info that could shed light on the dispute.

It appears from the docket Hall and Oates were in arbitration over some dispute. Typically, musical groups have their own contracts, and it would seem Hall believes Oates violated that deal. As for what it could be ... possibly a dispute over division of royalties, or it could be over Oates singing their songs in solo acts.

Hall decided to amp things up, going to Nashville Chancery Court and asking for a restraining order against his former partner ... a restraining order which the judge granted.

Fact is ... Hall and Oates have been doing their own thing, on and off for years.  Sometimes they reunited, but often performed solo. Although we don't know, it well could be Hall thinks Oates has no right to sing their songs during his concerts.

Oates has been touring this year, most recently in Arizona earlier this month.