Answer:
No error.
Step-by-step explanation:
Punctuation errors, be it in the use of the punctuation signs, or capitalizations, etc. forms one of the most important aspects of correct sentences. And not only that, the subject-verb agreement, the use of the adverbs and adjectives also constitute a correct sentence.
In the given sentence "[A]lthough Sonia dances gracefully, her brother Tomas moves clumsily", there is no error. The adverbs "gracefully" and "clumsily" are correct, describing the way the characters move.
Thus, there is no error in the given sentence.