Katherine Jackson -- The Michael Jackson Estate Buck Stops Here

Katherine Jackson has a problem she may not realize -- while she's raking money in from various Michael Jackson businesses, the judge in the MJ estate case could shut her out of a huge monthly allowance the MJ estate has been providing.

TMZ first reported ... Katherine and Joe Jackson sponsored a ritzy Michael Jackson event at the Beverly Hilton Hotel Saturday night -- with tickets going as high as $500 a pop -- and if there are profits, we're told some of that will line her pocket.

And then there's the book she's hawking -- "Never Can Say Goodbye" -- co-authored by Howard Mann, who made a fortune off of nude online gambling.

Mann tells us he's going into other businesses with Katherine as well. Roger Friedman from Showbiz411.com says he's seen a contract between Mann and Katherine which guarantees her $10,000 a month for promoting a book in the works, "The Katherine Jackson Story." Mann claims Katherine will net $10 mil from the book.

Now here's the problem ... When the judge in the Michael Jackson estate case signed off on Katherine getting more than $26,000 a month, it was based on need. If she's making money on the side -- especially making money off her late son -- it's likely the judge will no longer see the need to fill Katherine's wallet.

So it's coming down to a "Let's Make a Deal" decision. Katherine, do you want door #1 or door #2?