Two of my English Conversation students, to express the idea that they were busy, or occupied, recently used the term "occupated." ("I was occupated until seven o'clock.") I have never heard this word used before in this context, although I have seen it used to mean "occupy" ("The country was occupated by force").
One of the pitfalls of learning a new language is that accoutrements from one's native language invariably slip into common usage, out of sheer habit. For example, in English we say "cancel" an appointment. When I want to express this in French, I'm prone to use the verb canceler instead of the correct word, annuler. (Canceler falls under the category of the dreaded Anglicism.)
So what's the big deal--if you say "occupated" to mean "occupied", or canceler instead of annuler? People will still understand you. That's not the point. As annoying as they are, the grammar police provide a needed service--if only to alert us to deliberate or unconscious transgression of language, reminding us of its inherent malleability. Language changes, words disappear from use, new ones emerge to fit the times; it's a natural evolution. The result is often amusing, sometimes controversial, but always interesting, especially in fiction when it's done intentionally. (In my short story, "The Autobiographer", one of the characters uses adjectives as nouns ... e.g., "He's a bushy unreckognizable" or "It's a deplorable.")
