You could easily say that those rejected voter registrations where disallowed votes, but we don't know that all those rejected registrations represent voters that tried to vote. Either way it was a huge issue that resulted in a couple of different lawsuits against Paul Bettencourt and then his his successor Leo Vasquez - Harris Country Tax Assessor collectors. Vasquez settled the case and agreed to make some changes in the process. We have heard reports he's not adhering to the judgment very well.
Here's a good summation of the issue from Burnt Orange Report:
Republican-led Harris County Voter Registration Office Admits to Voter Suppression Tactics 10/27/09I have not heard of a change in votes - that would mean hacking wouldn't it?
For a great story on recent hacking of votes in D.C.
Voting Test Falls Victim to Hackers - NY Times 10/8/10