Akismet is blocking valid comments

I have two to three readers who comment quite regularly and frequently during the day. But in the last 24 hours Akismet is blocking all their comments. I have to go in and then unspam it for their comments to show up on the blog. Other readers have no problems in commenting.

Their comments are descriptive, more than 25 words and contain no links.

Any idea why I’m having problems with these two readers’ comments? Is there a way to resolve this issue?