The Simpsons -- Renewal Snag ... Key Actor Holding Out

Fox has announced "The Simpsons" -- which has run 26 seasons -- is coming back for another 2, but they may have jumped the gun because we've learned one of the key players has not signed on.

Sources close to the production tell TMZ the holdout has not reached an agreement. The sources would not say which actor is holding out, but we're told it's a key person in the mix.

We're also told the people who have signed on have all agreed to the same amount per episode and that is not an issue with the holdout. The sticking points in the past have had to do with back-end profits and merchandising.