I found the following over at the DC Metro Area Personal Injury Law Blog which provides a crisp summary regarding legal malpractice claims:

“Legal malpractice cases are often expensive to litigate and difficult to win. Three conditions must exist in order to prove legal malpractice:

• An attorney-client relationship existed;
• The attorney breached a duty he or she owed to the client; and
• The attorney’s wrongdoing caused the client harm.

The most common reasons for a legal malpractice suit are:

• The lawyer didn’t know the substantive law well enough;
• The lawyer failed to get a client’s consent  or to inform the client;
• The lawyer failed to calendar events;
• Not knowing or observing a deadline; and
• Insufficient discovery and/or investigation.”