While an adverb ending with -ly has no grammatical problem, many consider it as bad style. Straight from "On Writing Well, 5th Edition" by William Zinsser: "Most adverbs are unnecessary. You will clutter your sentence and annoy the reader if you choose a verb that has a specific meaning and then add an adverb that carries the same meaning. Don't tell us that the radio blared loudly - "blare" connotes loudness. Don't write that someone clenched his teeth tightly - there's no other way to clench teeth. Again and again in careless writing, strong verbs are weakened by redundant adverbs."

So instead of using an adverb that modifies a verb, make sure you have a strong verb instead.