It's a grammatical error related to the incorrect use of an adjective.
People may confuse the adjective "temporary" with the adverb "temporarily". They mistakenly use "temporary", an adjective, to modify the adjective "closed", when they actually need "temporarily", an adverb, to describe the state of being "closed".
The correct form is "temporarily closed". This is because "temporarily" is an adverb that modifies the adjective "closed", indicating the duration of the closure.
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