Instead of Is there any grammar mistake in the following sentence?
you might say Are there any grammar mistakes....
"Statements must be provided to any interested party that so requests them from the administrator within ten days."
The sentence seems to be free of any grammatical errors.
"So" in that sentence serves as a formality. It might be replaced with a more familiar term such as "might" (but then request instead of requests). It maintains subject-verb agreement to state the sentence in that manner. "to any interested party that so requests" since party is singular and requests is the singular form of the verb.
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