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Morgan Freeman ain't happy with Zach Braff -- and last night, the Hollywood legend told TMZ ... the "Scrubs" actor SCREWED UP BIG TIME when he went to the Internet and said M.F. was a fraud.

The back story is a little complicated -- but we'll boil it down for you ...

Braff has been under fire recently for launching a Kickstarter campaign to raise money for a new movie he wants to make. Critics say Braff is abusing Kickstarter -- a crowdfunding website -- because it's intended to help struggling entrepreneurs who generally don't have access to people with deep pockets ... not huge, rich stars like Zach.

So ... Braff hosted an online Q&A session to address the controversy -- and, while trying to explain the importance of being honest with his fans, dragged Freeman into the controversy.

"People can smell bulls**t a mile away ... look at what happened when Morgan Freeman did that AMA on reddit," Braff said.

FYI -- an AMA (or Ask Me Anything) is an online chat session where the person agrees to personally and honestly answer ANYTHING from fans. After Freeman's lackluster AMA session recently, people suspected Freeman's rep was actually answering the questions for him.

"There was huge backlash because it was so clearly a film publicist answering for [Freeman]," Braff said.

Last night, Freeman finally responded to Braff's allegations -- and it's clear, Freeman no likey.