You are assuming that it will return matches in your code. I would change your code slightly to allow the test of successfully finding matches.
Here is an example to test for matches
dim SearchData as string = txtSearch.text.trim
dim RegExString as string = "\b\w*[a-z]\b"
dim RegExMatch as match = Regex.Match(SearchData, RegExString)
if RegExMatch.sucess = true then